发动机分电器内断电器周期性地接通和切断低压电路。
参考答案：对
The poor little boy ______ by his heartless parents was seen begging in the street.
A．abandoning
B．to be abandoned
C．having abandoned
D．abandoned
常用的一般防护安全用具有（）。
A.携带型接地线
B.临时遮栏
C.安全带
D.警告牌和标示牌
E.防护目镜
