TOEFL Listening: ETS-TOEFL听力机经 - 53HJJVTT721ZL8MVP$

Why does a student mention global warming and greenhouse gases? A. To support the professor's claim about problems with current levels of crude oil usage B. To find out what the original motivation was for the development of thermal depolymerization C. To raise a question about the potential environmental impact of thermal depolymerization D. To point out an advantage of using inorganic waste to create crude oil