装拆接地线的顺序是先装中间相后装两边相。
参考答案：错
It is thought that one billion people I the world, _____is half the word’s workers, earn their living by farming.
A．if
B．that
C．which
D．what
二氧化碳放空阀的位号是（）。
A.PV-0704
B.PV-0705
C.PV-0717B
D.PV-0711B
