单项选择题
A.0.5*额定电压 B.0.6*额定电压 C.0.7*额定电压 D.0.8*额定电压
A.≤10s B.≤15s C.≤20s D.≤30s
A.≤3s B.≤4s C.≤5s D.≤6s