The correct answer is C.
The statement "Every person should make it a priority to serve at least two hours per week." is not objective and is not a crucial detail.
The point of the article is that community service is beneficial. However, it is not a fact that serving at least two hours a week is necessary. More or less time devoted to service might be better -- but the author is offering no objective proof to this weekly two-hour requirement.
Therefore, this sentence is the least important sentence in the entire paragraph. It can be deleted without losing any meaning regarding the importance of community service.