Hardly ______ when a loud explosion was heard.
A.the train had started
B.the train had been started
C.had the train started
D.the train started
第5题
继电器保护规程规定:过电流继电器返回系数应不低于0.85;低压继电器的返回系数应不大于()。
A)1.05;
B)1.25;
C)1.5;
D)2.5
第8题
A、1.5
B、2
C、2.5
D、3
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