【单选题】在三相异步电动机的正反转控制电路中,正转接触器KM1和反转接触器KM2之间的互锁作用是由( )连接方法实现的。
A.
KM1的线圈与KM2的动断(常闭)辅助触点串联,KM2的线圈与KM1的动断(常闭)辅助触点串联
B.
KM1的线圈与KM2的动合(常开)触点串联,KM2的线圈与KM1的动合(常开)触点串联
C.
KM1的线圈与KM2的动断(常闭)触点并联,KM2的线圈与KM1的动断(常闭)触点并联
D.
KM1的线圈与KM2的动合(常开)触点并联,KM2的线圈与KM1的动合(常开)触点并联
【单选题】If someone says, "It cannot hurt to ask." he means ______________.
A.
it's a good idea to ask.
B.
he doesn't want to ask.
C.
it will hurt if he asks.
D.
he's not sure whether to ask or not.
【单选题】继发型肺结核与原发性肺结核的主要不同点是
【单选题】Mr. Zhang is the best music teacher in our school, but he has hurt his left foot and cannot ________tomorrow’s concert.
【单选题】. The best music teacher in the school has hurt his left foot and cannot ______ tomorrow’s concert.
【单选题】按钮联锁正反转控制电路的优点是操作方便,缺点是容易产生电源两相短路事故。在实际工作中,经常采用( )正反转控制电路。
【单选题】188. 按钮联锁正反转控制电路的优点是操作方便,缺点是容易产生电源两相短路事故。 在实际工作中,经常采用( )正反转控制电路。
【单选题】近年来兴起的慕课( mooc)指的是( )