翻译并解析答案w: You don't believe in diet, do you?m: There is noth

翻译并解析答案
w: You don't believe in diet, do you?
m: There is nothing wrong with themper se(本身), but they have to be combine with exercise to do any good.
Q: What does the man mean?
(A) The woman's health has improved.
(B) He does not have enough energy to exercise.
(C) By themselves diets are not useful
(D) Diets can be harmful.
答案是c,请翻译并解析