Nobody knows broke into the house last night and stole the important papers.A. who was it

问题补充：

Nobody knows broke into the house last night and stole the important papers.

A. who was it that

B. it was who that

C. who it was that

D. that it was who

答案：

A. who was it that

B. it was who that

(答案→)C. who it was that

D. that it was who

解析：考查强调句型。本题考查的是强调句型的特殊疑问句，把是对人进行提问的特殊疑问句，作为宾语从句，使用陈述语气，特殊疑问词放在前面，后面使用陈述语序。句意：没有人知道是闯进了房子偷走了重要的论文。故C正确。