 So, since we just did that lecture, let's try to, that lecture topic, let's try to classify these as homo-atomic or heterotomic. So I guess the question says, classify the following molecules as homo-atomic or heterotomic. So what do you got here? You got oxygen, which is O2, so they're giving you the molecular formula here, O2, carbon dioxide, which is CO2, and carbon monoxide, which is CO. So later you're going to learn how to draw these molecules and understand why they're built the way they are. But for right now, we just want to know whether all of the atoms in the molecule are the same, which is homo-atomic, or if some atoms in the molecule are different than other atoms in the molecule, of course. So if we look at O2 here, we know that there's, well this subscript means that there's two oxygens stuck together, so they're bonded together. So there's just two oxygens, so that's a homo-atomic molecule. So CO2, remember when it's the whole formula here, it means that all these atoms are bonded together. So of course that means that there's one carbon atom and two oxygen atoms bonded together to make up the molecule, carbon dioxide, or CO2. So that means that there's different types of atoms that are necessary to construct carbon dioxide, so we call that a hetero-atomic molecule. And then carbon monoxide, another common molecule, actually a very interesting structure when we get to that. But you can see here it's composed of one carbon atom and one oxygen atom. So of course that's not both the same atom, so that's also hetero-atomic. So are there any questions on this one? So pretty straightforward I guess, we'll do one more problem on this, and if there are any questions then you guys can ask them that, okay? So you want to cool with that one? Like I said, I think pretty straightforward.