a man knows what is not to be done will he succeed in doing what is to be done.A. What i

问题补充：

a man knows what is not to be done, will he succeed in doing what is to be done.

A. What if

B. If only

C. As if

D. Only if

答案：

A. What if

B. If only

C. As if

(答案→)D. Only if

解析：考查倒装句。Only放在句首并强调状语时，使用部分倒装句。本题only 放在了句首，且if a man knows what is not to be done是一个条件状语从句，所以选D；句意：只有当一个人知道了不应该做的事情，他才能成功地做应该被做的事情。