问题补充：
Listening to loud music at rock concerts caused hearing loss in some teenagers.
A. is
B. are
C. has
D. have
答案：
A. is
B. are
(答案→)C. has
D. have
解析：考察主谓一致，该句的主语是listening to loud music所以后面的谓语动词用单数，主语个动词cause之间是主动关系，所以选择C
句意为，在摇滚音乐会现场听吵闹的音乐已经导致了很多年轻人听力的损伤
