 Welcome to Learning English, a daily 30-minute program from the Voice of America. I'm Ashley Thompson. And I'm Dan Novak. This program is designed for English learners. So we speak a little slower, and we use words and phrases, especially written for people learning English. On today's program, I report on the spread of Islamist groups in West Africa. John Russell has a story on a new study about the mysterious planet Eris. Brian Lin has the science report on an AI robot that could be able to produce oxygen on Mars. Later, Andrew Smith and Jill Robbins present the lesson of the day. But first, Islamist groups linked to al-Qaeda and the Islamic State have been spreading across Africa for years. The groups came from the large area south of the Sahara Desert called the Sahel. They are spreading into wealthier West African coastal nations like Benin. Militants once were believed to want to use coastal nations like Benin, Togo, and Ghana as basis for attacks on Sahel governments. Now the militant groups are strengthening. Benin has been the hardest hit. This year it had more than 10 times the number of violent incidents involving Islamists than Togo did. That information comes from the armed conflict location and event data project. Attacks by militant Islamists, or jihadis, against civilians in Benin went from more than 30 to about 80. The overall number of incidents involving jihadi groups rose by more than 70%. The jihadis' activity in Benin is mostly in the north of the country. There they try to recruit people and create division within local populations. Residents of one small town told the Associated Press recently that civilians can no longer move freely. People in Materi live in fear because of the jihadi threat. The fighters place explosives and carry out kidnappings in the area. They aim to make people lose trust in the government. The government has put in place a curfew and a ban on gatherings. I can't sleep at night. We're not free to travel to move, Materi resident Florence Bhatti said. People are too afraid. People are being displaced from their homes as attacks increase. Some people fear a humanitarian crisis. In August, more than 12,000 people were displaced from their homes in the Atacora and neighboring Alibari states. That is an increase from about 5,000 in March, the United Nations said. The violence is also pushing people from their farms. The UN estimates that tens of thousands of people could face hunger. The government is trying to improve the situation by placing additional security forces along the borders and hiring more soldiers. Local people in the north say they have seen increases in soldiers but say the army is under-equipped and is sometimes late when answering attacks. Neighboring Burkina Faso, Niger and Mali are being overrun by violence. The nations ousted French troops after the militaries there seized power. But Benin is still open to help from its former colonial power, which left in 1960. The French do not have a permanent base in the country. At Benin's request, however, French troops can take part in training programs with Beninese soldiers, a French military spokesman said. People in the north told AP that Benin's government is also trying to hide the level of the crisis. The government has limited freedom of speech and arrested reporters who cover insecurity. Local officials have said the problem does not go beyond the border with Burkina Faso. There is no terrorist, no movement, no organization, no group that has settled or tried to settle in our department said Robert Wimbocasa, the mayor of Materi. Benin is an agricultural nation of 13 million people. It has invested billions of dollars in culture and tourism. It is also building a $1.5 billion industrial area outside of the city of Kotenu, aimed at creating 300,000 jobs by 2030. The lack of information has left people in other parts of the country unaware of the security problems in the north. People in Kotenu said they did not know about the jihadi problem. They did not believe the news or said that it was a problem limited to neighboring countries. Rights groups say the government is attempting to control information while arresting people believed to be working with the jihadis. The groups say the government is pushing people into the militants' hands. Ares, a very small planet similar in size to Pluto, has remained a mystery since its discovery in 2005. The American Space Agency, NASA, explored Pluto in 2015 using its spacecraft New Horizons. Ares, about 40% farther from the sun, has never been visited. But scientists are gaining a fuller understanding of Ares and its differences with Pluto. A recent study provides details about the little planet's structure and composition based on its relationship with its moon Dysnomia. Ares, researchers said recently, appears to have a rocky inside under a level of ice. Pluto also has an icy outside with rock below, but has a higher ice content and is thought to have an underground liquid ocean. We already knew that Ares is more rock-rich than Pluto but what we didn't know was whether Ares had separated the rock from the ice said study lead writer Francis Nemo of the University of California, Santa Cruz. The study appeared in the publication Science Advances. Nemo said Ares got hot enough at some point in history to melt and all the rock sank to the center. The ice is not motionless but is experiencing a slow churning motion driven by leftover heat from the inside. Most likely there is no liquid ocean inside Ares, Nemo said. Ares has a diameter of about 2,326 kilometers. Pluto's is a little bigger at about 2,370 kilometers. Both are smaller than the Earth's moon which has a diameter of 3,475 kilometers. Because of the greater amount of rock which is denser than ice Ares has about 25% more mass than Pluto. As I like to think of it, take Pluto and add every single asteroid in the asteroid belt and you get Ares, said study co-writer Mike Brown, one of the three scientists who discovered Ares. Ares orbits at an average of about 68 times further from the Sun than Earth. It completes a full turn around the Sun in 557 years. The moon, dysnomia, is about 700 kilometers in diameter and made up mostly of ice. Just like the Earth-Moon system, tides on Ares slowly push dysnomia away and slow down the spin of Ares. This process has gone to completion. Ares and dysnomia always present the same face to the other, Nemo said. Pluto has this same system with its moon Sharon, while the Earth-Moon system differs. The moon always presents the same face to the Earth, but the Earth does not return the favor, Nemo said. Ares and Pluto are located beyond Neptune, the outermost of our solar system's eight bigger planets. The International Astronomical Union, which sets definitions for planetary science, recognizes five very small planets known as dwarf planets, Ceres, Helmia, and Maki Maki, in addition to Ares and Pluto. Ares is the most massive of them. The new findings fill in some questions about Ares. Each of the largest dwarf planets is unique, and we should be cautious about inferring too much from what we know about Pluto, Brown said. I'm John Russell. Chinese researchers say they have built an artificial intelligence, AI, robot, that can carry out chemical reactions to produce oxygen from water on Mars. The system could be another way for space travelers in the future to make much needed oxygen on Mars. Humans visiting the red planet will need oxygen to support life. The gas could also be used to make rocket fuel, which is difficult to transport to space. Scientists have already established from multiple studies that Mars contains large amounts of water. Most of the water exists in the form of ice. Developers of the new robot system in China say it can be used to release oxygen from the planet's water supply. Scientists at the University of Science and Technology of China in Hafe led the research. The team explored whether an AI robot could use materials found on Mars to produce catalysts to break down water and release oxygen. A catalyst is a substance that permits certain chemical reactions to happen. Experiments were carried out on meteorites that either came from Mars or contained materials similar to the Martian surface. The researchers said the robot chemist first used an acid and chemical mixture to separate and examine materials contained in the meteorites. It identified several different metallic elements including iron, nickel, magnesium and aluminum. The machine then worked to identify different molecules that could be produced from meteorite materials. The team said the system found more than 3.7 million possible molecule combinations. The robot used that data to predict which catalysts would be able to split water molecules to produce oxygen. The catalyst chosen as the best fit was able to operate at minus 37 degrees Celsius. This temperature is similar to current conditions on Mars. A press release announcing the experimental findings said the AI chemist was able to complete the whole process without human involvement in just two months. The release claimed such an operation would take 2,000 years for a human chemist to finish. The publication Nature's Synthesis reported the full results of the study. The study's lead writer, Jun Zhang, told the website space.com that as a boy he often dreamed of being able to one day travel in space. So when we finally saw that the catalysts made by the robot could actually produce oxygen by splitting water molecules, I felt like my dream was coming true. I even started to imagine that I myself will live on Mars in the future. The researchers said they plan next to test whether their AI system performs well under a series of other conditions besides temperature found on Mars. A report explaining the study's results in Nature notes, Zhang suggests that for every square meter of Martian material, his group's system could produce nearly 60 grams of oxygen per hour. The researchers say this level of production could remove the need for future astronauts to transport oxygen from Earth. The robot can work continuously for years, Zhang said. Zhang told Nature he thinks his team's robotic system could also be used to produce other useful catalysts on Mars. This could include processes for making substances to support the growth of plants that could be used to produce food for astronauts. Different chemicals can be made by this robot, Zhang said. He noted that Mars might also not be the only place where it could find other uses, suggesting the moon as another possibility. I'm Brian Lin. Brian Lin is here now to talk more about his science report. Thanks for joining me, Brian. Sure, Dan. Glad to be here. This week you described an AI system scientists say can produce oxygen from water without any human help. The research centered on this system being used in the future on Mars. Are other oxygen-making technologies also being developed for use in space? Yes, so we learned that the AI system created by Chinese researchers could provide enough oxygen to support astronauts spending long periods on Mars. But there are other systems under development. Earlier this year, for example, we reported on a device shown to be able to convert carbon dioxide from the Mars atmosphere, essentially from air into oxygen. And this system has been tested on NASA's Perseverance rover on Mars. So far, the testing has involved very small amounts of oxygen, but developers are confident such a system can be scaled up to provide much larger levels. Always interesting having you on, Brian. Thanks for joining me. You're welcome, Dan. Thank you. My name is Anna Matteo. My name is Andrew Smith. And my name is Jill Robbins. You're listening to The Lesson of the Day on the Learning English Podcast. Welcome to the part of the show where we help you do more with our series Let's Learn English. This series shows Anna Matteo in her work and life in Washington, D.C. In Lesson 37 of the series, Anna finds a backpack outside her office building and tries to find the person it belongs to. Let's listen. You know, I am from the country. And sometimes I miss it. But I really like life in the city. I love the city. Oh, look, someone lost a bag. Maybe it's theirs. Excuse me. Is this bag yours? No, it's not mine. It might be hers. Thank you. Hello. Is this bag yours? Yes, that's mine. These are all my travel things. Thank you. Thank you. Luckily for this traveler, Anna found his bag and brought it to him. Anna was thinking to herself. I wonder whose bag it is. I don't know. Anna was thinking to herself. I wonder whose bag this is. That's whose, spelled W-H-O-S-E, which refers to possession. That means to whom the object or idea belongs. Right. So if you find something and you're not sure whose it is, one thing you can ask is, Whose is this? Remember that this word, whose, is spelled differently than the contraction of the two words, who is. Those two words form a subject and verb, like this. Who's the President of the United States? The contraction and the possessive adjective both sound the same. They are both pronounced with the sound of the letter Z at the end. Whose bag is this? Who's the President of the United States? And when we talk about to whom something belongs, we use possessive pronouns. We heard these when Anna was trying to find out whose bag she found. Oh, look. Someone lost a bag. Maybe it's theirs. Excuse me. Is this bag yours? No, it's not mine. It might be hers. Thank you. Excuse me. Is this bag yours? No, it's not mine. It might be his. Thank you. Hello. Is this bag yours? Yes, that's mine. These are all my travel things. Thank you. Thank you. You'll notice that these possessive pronouns sound almost the same as possessive adjectives. For example, the adjective form of the pronoun you is your. Like when we say this is your bag. And then for the possessive pronoun, we just add the letter S. For example, this bag is yours. But notice that the S at the end sounds like the letter Z. Yours. If you listen carefully, you can hear a bit of the sound of the letter S at the end of a word like yours. So the sound of Z is not as strong or as long as in a word like zero. Instead, it's more like a Z with a little S at the end. Yours. Now listen to these five possessive pronouns. Yours, his, hers, ours, theirs. We'll listen to a chant at the end of today's lesson of the day to give you a fun way to practice saying these possessive pronouns. Oh, we will. Whose idea was that? That idea was mine. Well, I'm not surprised. Let's go back to lesson 37 and see what the owner of the bag and Anna talk about. Are you okay? You seem nervous. Well, this is my first visit to Washington, D.C. I'm from a small town in the country. I feel a little lost. I'm from the country, too. And I understand when I first came here, I felt lost all the time. So do you like living in the country or in the city? I like to live in the city. Why? The city is exciting. It has more culture than the country. There are many museums and restaurants. Every night there's theater and music. And there are more jobs. That is why I'm here. Well, I agree. There is more culture in the city. And there might be more jobs, but the country has more nature. It's peaceful and beautiful. There are more trees and mountains. The air is clean. You can go hiking and camping. The city is not beautiful. It's noisy and dirty. I disagree. I think all the different buildings are beautiful. And I like to watch all the different people. Anna and the man from the country. And we should note that when the man uses the word country, he means he is from a rural area, not a city. It does not mean he's from a foreign country. Good point. Anna and the man from the country are talking about which kind of place they prefer. Prefer is a verb. It means to like something more compared to another thing. Anna prefers the city, while the man prefers the country. So they are talking about their preferences. Preference is a noun. It means the thing or the choice that you like more. And we can use it or the verb form to form a question. For example, we can ask, Which do you prefer, the city or the country? Do you already know or have mentioned the choices you can just ask? Do you have a preference? Or you can ask, Do you have a preference between the two? Anna and the man prefer different things. In another lesson of the day, we'll listen to more of lesson 37 of Let's Learn English and find out if Anna and the man continue to disagree or if they share some preferences. And here's a question for our listeners. Do you have a preference between living in the city or the country? You can let us know which you prefer by writing to us at LearningEnglishatvoanews.com. So Andrew, we're almost out of time. How about we listen to that chant with possessive pronouns? Okay, let's do it. And special thanks to my friend Jennifer, who helped record the chant. Here it is. It's mine. It's mine. Is everything yours? Not everything's mine. This one's yours. And that one's hers. And those are his. But what about these? These are mine. But what about those? Those are mine. Are you gonna share? Of course I'll share. Whenever we share, It's not just yours. It's not just mine. It's yours and mine. It's yours and mine. It's yours and mine. It's yours and mine. And together, it's ours. I'd like the ending of that chant. It can feel good to share with others. And if you enjoy the lesson of the day on the Learning English podcast, we hope you will share it with other people. You can do that by finding us on Facebook, YouTube, and Instagram. And you can find all of the Let's Learn English series on our website, learningenglish.voanews.com. Thanks for listening. I'm Dr. Jill. And I'm Andrew Smith. And that's our program for today. Join us again tomorrow to keep Learning English through stories from around the world. I'm Ashley Thompson. And I'm Dan Novak.