I use the power of elimination for multiple choice questions. Next I underline the main things that the question is asking, so I won't get confused. Underline the keywords "not likely" and "population". I would assume that "c" is the answer, but I could be wrong.....it's only an assumption. Since dolphins are an aquatic mammal "c"~drought would be the obvious choice. (for me anyways. If you don't agree with my choice that's okay. My process for multiple choice questions is a good one.)
