C). While fear can be useful in protecting us against danger, anxiety is not always helpful.
Explanation:
In the given excerpt, the third option i.e. 'while fear...helpful' most aptly conveys the key idea of the segment 'Why We Worry' as it shows how fear can be beneficial in defending dangers ahead and preserve us while anxiety may lead us in danger. Thus, the central idea that the author is conveying is that one can be fearful as it shows something is happening while one should not worry about anything as it signals of something actually not happening. Thus, <u>option C</u> is the correct answer.
