港口门机起升机构的线路中，除了过流、零压、连锁等保护外，还设有（）、限位保护。
A、过电压
B、低电压
C、超负荷
D、差动
参考答案：C
It was with great excitement one morning in July ____ the young man got the news that he was admitted to the university of his choice.
A．when
B．who
C．that
D．which
通电螺线管外部周围的磁场和________的磁场一样，它两端的极性跟______的方向有关。
