一道题，请回头看一下！

It’s necessary to be prepared for a job interview. ______ the answers ready will be of great help. (北京’05)

A. To have had   B. Having had   C. Have   D. Having

[考点说明] 动词-ing 形式可以作句子的主语。

请问 having done 可否做主语？

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having done一般在状语从句中表过去。作主语的没看到过。

having done 应该不能做主语

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