问题补充：
to find the book from the library, she decided to turn to her professor for help.
A. Failed
B. To fail
C. Having failed
D. Being failed
答案：
A. Failed
B. To fail
(答案→)C. Having failed
D. Being failed
解析：句意：从图书馆没有找到那本书，她决定向她的教授求助。现在分词作原因状语。上下文所
说的事情发生的时间显然有时间的先后。故要用现在分词的完成式=Because she had failed to find the book
from the library…
