I keep dogs for protection, but now I keep them as pets.
A. would rather
B. had better
C. used to
D. have to
网友回答
A. would rather
B. had better
(答案→)C. used to
D. have to
解析：“我曾经养狗为看家，但现在我把它们当宠物。”说明是现在养狗与过去养狗的区别，故选C。used to + v.：过去曾（而现在不再）做（用于过去持续或经常发生的事）