How does the overall structure of “conservation as a national duty” facilitate the development of ideas in the speech?
a. the descriptive structure provides detailed information about each type of natural resource and why it is important.
b. the chronological structure explains how the use of natural resources has evolved and expanded over time.
c. the problem-and-solution structure establishes how the problem came to be, describes the potential outcomes, and suggests actions for resolution.
d. the cause-and-effect structure tells how each type of natural resource is used and explains the specific effects of the resources’ usage on the environment.

I believe the correct answer is C. The problem-and-solution structure establishes how the problem came to be, describes the potential outcomes, and suggests actions for resolution.

Explanation:

Roosevelt's famous speech about conservation does indeed refer to history - both American and the whole world's history. But it only does so in order to provide a deeper insight into the nature of the problem. He uses historic references to outline the problem (exhaustion of resources). Then, he proposes solutions to this problem.

True, America's natural resources were a great driver of economic and national growth. However, according to Roosevelt, if Americans don't adopt a new perspective and start thinking about their posterity, soon there won't be much left to work with. There are two categories of resources, each of which require a separate course of action:

to persuade readers which is answer c