单项选择题
A.3个月 B.6个月 C.12个月 D.18个月
A.0.5 B.0.4 C.0.7 D.1.0
A.0.8 B.0.5 C.1 D.0.9
A.串联 B.并联 C.级联 D.串、并联
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