It’s necessary to be prepared for a job interview.the answers ready will be of great help.

问题补充：

It’s necessary to be prepared for a job interview.the answers ready will be of great help.

A. To have had

B. Having had

C. Have

D. Having

答案：

A. To have had

B. Having had

C. Have

(答案→)D. Having

解析：动名词短语作主语。having the answer ready意为“把答案准备好”。