单项选择题
An indicator on the main switchboard should show （） the emergency battery is in service or not.
A.that B.when C.if D.whether
单项选择题 When a sudden increase in steam demand comes to normal, the drum pressure will and water level in the drum will（）.
单项选择题 If a hydraulic pump is overheating, the cause may be （）.
单项选择题 The motor for the fresh water pump （）.
