making cars run on less fuel finding more sites for copper mines making ocean liners bigger and faster replacing human workers with robots
I gave my students this multiple choice question: Of these research projects, which is the best choice for a student who is interested in environmental issues to study?

Only one answer is correct among these 4 choices:
- making cars run on less fuel
- finding more sites for copper mines
- making ocean liners bigger and faster
- replacing human workers with robots

Could you tell me which one is correct?

making cars run on less fuel