单项选择题
A.1 B.2 C.3 D.0
A.1次/1个月 B.1次/2个月 C.1次/2天 D.1次/6个月
A.1次/2天 B.1次/2个月 C.1次/3个月 D.1次/5个月
A.1次/1个月 B.1次/2个月 C.1次/2天 D.1次/4个月
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