VVVF控制是指逆变器输出（）可变的控制。
参考答案：电压和频率
Something _______ wrong with the machine, and it _______ not work.
A．being; could
B．going; should
C．were; might
D．went; would
10（6）kV架空线路跨越不通航河流且在最大弛度时，导线至水面的距离不应小于（）m。
A.3
B.4
C.5
D.6
