试品绝缘电阻的测量值获取需加压（）。
A、15s
B、30s
C、45s
D、60s
参考答案：D
电解质压降占整个槽电压的百分比为（）
A、10~15%
B、20~25%
C、35~40%
D、40~45%
Hardly ____ the airport when the plane took off.
A．I had arrived at
B．had I arrived
C．had I reached
D．I had got to
