单项选择题
(A)110V (B)220V (C)100V (D)200V
(A)5s (B)57.5s (C)87.5s (D)110s
(A)变小 (B)变大 (C)不变 (D)无穷大
(A)18个 (B)19个 (C)20个 (D)21个
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