 This lesson four deals particularly with energy and the environment. As I mentioned before in the unit overview, this lesson is divided into three parts. Part A is basically looking at the products that are formed when we burn fossil fuels and the environmental effects of these fossil fuels products. And in the part B, we are going to look at the global effects, global warming. We will also look at in part C like acid rain and again ozone layer destruction up above in the stratosphere and ozone formation because of the chemicals that we emit, the pollutants that we emit at the ground level. Ozone is formed over at the ground level, which is not supposed to be there. Ozone is supposed to be there in the stratosphere, which we are destroying by some of the actions. And where it is not supposed to be, we are forming. So this lesson basically talks about some of those aspects. Go through this part A, part B and part C and together there will be one quiz for this lesson. And after you complete all parts and do all the practice quizzes for a study mate questions, different activities and then actually part the lesson five will also be included for your next exam. Although we call this unit, it consists only of one lesson. So next unit lessons also will be included in the next exam.