The correct answer is A. The U.S. should work harder to compete in the development of clean energy technologies.
Explanation:
Chu says that there are still so many things that the US can do in order to be one of the main participants in creating clean energy technologies. There is still a long way before they can be on par with some other competitors in this field and she feels is US's duty being such an important country in the world to do more about this issue.
