若通过一导体的电流增加一倍，则电功率是原来的（）倍。
A、1
B、2
C、4
D、8
参考答案：C
It was not until the 18th century that man realized that the whole of the brain was involved in the working of the mind， ？
A．was it
B．wasn’t it
C．did they
D．didn’t they
下列关于F1力臂的作图中，正确的是[ ]
A.
B.
C.
D.
