The staff are excited that they have succeeded in what they to do three months ago.A. set

问题补充：

The staff are excited that they have succeeded in what they to do three months ago.

A. set off

B. set about

C. set out

D. set up

答案：

A. set off

B. set about

(答案→)C. set out

D. set up

解析：考查动词短语：A. set off出发，引爆，引发，B. set about开始，后面接doing，C. set out开始，后面接不定式， D. set up建立，句意：大家很兴奋因为他们成功的完成了3个月前开始做的事情。因为搭配的是不定式，所以选C。