问题
选择题
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
答案
答案：C
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。