he was seriously ill I wouldn’t have told him the truth.A. If I knewB. If I knowC. Had I

问题补充：

he was seriously ill, I wouldn’t have told him the truth.

A. If I knew

B. If I know

C. Had I known

D. Did I know

答案：

A. If I knew

B. If I know

(答案→)C. Had I known

D. Did I know

解析：考查含有if条件状语从句的虚拟语气。根据wouldn’t have told，可知指的是过去情况，所以if从句要用过去完成时态，即if I had known he was seriously ill,助动词had可以提到句首，省略if ，构成部分倒装，即had I known he was seriously ill。所以选C。