对于明设的燃气管道，采用( )固定方式是错误的。
A．焊接 B．吊卡 C．管卡 D．管支架
参考答案：A
It was hard for him to learn English in a family, in which _____ of the parents spoke the language.
A．none
B．neither
C．both
D．Each
A．时刻t线圈中电流的瞬时值icosωt
B．线圈中电流的有效值I
C．线圈中电流的有效值I=
D．线圈消耗的电功率P
cosωt
