Who helped you clean the classroom yesterday?- . I cleaned it all by myself.A. Ever

问题补充：

--- Who helped you clean the classroom yesterday?

--- . I cleaned it all by myself.

A. Everybody

B. Somebody

C. Nobody

D. Anybody

答案：

A. Everybody

B. Somebody

(答案→)C. Nobody

D. Anybody

解析：Everybody每个人；Somebody一些人；Nobody没有人；Anybody任何人，用于否定及疑问句中。句意：昨天谁帮助你打扫了教室？结合下文，我自己全部打扫了。可知选C。