C. Other countries are also using wind power as a source of energy.
Explanation:
This is the detail that is least supportive of the main idea. In the main idea, the author states that wind power is becoming an increasingly popular source of renewable energy in the United States. Options A, B and D give examples of how we can know that this is the case. However, option C, although it deals with the topic of wind power, discusses only what the case is in other countries, which does not give the reader useful information that supports the main idea.
