单项选择题
A.无烟煤 B.烟煤 C.褐煤 D.贫煤
A.电阻串联 B.电阻并联 C.电阻混联 D.都不是
A.50% B.60% C.70% D.80%
A.2MΩ B.1.5MΩ C.1MΩ D.0.5MΩ
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