单选题
Joan didn't go to the party last night because she ______the baby for her sister until 9: 30.
A、
must have looked after
B、
would have to looked after
C、
had to look after
D、
should have looked after
【正确答案】
C
【答案解析】
解析：本题考查句子时态。题干包含由because引导的原因状语从句，主句表示结果，从句表示原因，主从句时态应前后照应，所以用一般过去时，故答案为[C]项。
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