【题目】___________________, the experiment will be successful.
A.If carefully doing
B.If it was done carefully
C.If carefully done
D.If doing carefully

【答案】C
【解析】句意：这个实验如果认真被做就会成功。句中if引导的条件状语从句中，省略了主语和be动词，主语experiment与动词do之间是被动关系要用被动语态，完整句子应是：If the experiment is done carefully，故选C.