________, the scientists must keep the experiment under control and take down all the records carefully.

　　[A]: When to carry out laboratory work

　　[B]: When to be carry out laboratory work

　　[C]: When carrying out laboratory work

　　[D]: When carried out laboratory work

　　【世博精解】：carry out实现；完成；实行carry out one's plan实行自己的计划I have carried out my work.我已经完成了我的工作。

　　“When carrying out laboratory work”相当于一句时间壮语从句“When they are carrying out laboratory work.”

　　答案：C