问题补充：
Some policemen should be sent to them the animals.
A. prevent; to kill
B. stop; killing
C. keep; to kill
D. keep; killing
答案：
A. prevent; to kill
(答案→)B. stop; killing
C. keep; to kill
D. keep; killing
解析：句意：警察应该被派去阻止他们杀害动物。阻止某人做某事，用stop…(from)doing;prevent…(from)doing;keep…from doing.所以选B。
