每次爆破作业前，爆破工必须做电爆网络全电阻检查。（）
参考答案：对
The teacher assigned the task to the three boys and ________ did his share.
A．any
B．all
C．every
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
