Which of the Following Statements Regarding the Challenge of Countering

Which of the following statements regarding the challenge of countering extremism is most accurate?

A) Coercive measures alone are only marginally successful.
B) Strong military retaliation is very effective.
C) Repressing adherents of extremist sentiment is a highly effective option.
D) Both "strong military retaliation is very effective" and "repressing adherents of extremist sentiment is a highly effective option."