Question

13. A new technique_________, the yields as a whole increased by 20 percent.

A.working out

B.having worked out

C.having been worked out

D.to have been worked out

Answer 1

C

解析:

该题考查现在分词短语作状语的用法，由题意知“新技术应是被钻研出”，此处应用其被动语态形式，即“having been+过去分词”。?

答案：C?