The correct answer is B.
The United States and China would cooperate and try to find a solution to the problem regarding energy crisis. This problem affects both countries at the same time as both are the largest consumers of energy in the world.
Unless these two countries cooperate, the problem would not be solved. The climatic change is a big problem and both nations have to deal with its consequences. Also, dependence on foreign oil is not a solution for energy sources as it involves political involvement with different countries.
Obama tries to state that a cooperation between China and the United States is useful and necessary because the problems they are facing are global ones, and both countries would benefit from a solution.