Earth is believed by an object the size of Mars at some point in the distant past
before its surface cooled．
A. to be hit
B. to have hit
C. to have been hit
D. to hit
网友回答
A. to be hit
B. to have hit
(答案→)C. to have been hit
D. to hit
解析：考查非谓语动词。根据句意可知事情已经发生，故用不定式的完成式，earth与hit为被动关系，故用被动，选C。