单项选择题
The alternating current generator supplying a load has a voltage drop resulted from the loadWhen the load has a lagging power factor this voltage drop （）.
A.is small B.may be neglected C.is useful D.is considerable
单项选择题 After the trouble of the automatic control system has been completely eliminated, assistance is （） required.
单项选择题 （） is the actual value of the controlled condition.
单项选择题 Which of the following marine examples belongs to the open loop control system?（）
