单项选择题
When preparing an engine for water temperature（）
A.should be kept at a proper level by a cooler B.should be raised to about 80℃ by a heater C.should be raised gradually D.should be lowered to about 60℃
单项选择题 When stand-by engine instructions have been received, it’s necessary to make it sure that all valves in the various systems are（）
单项选择题 The monitoring function may serve all of the following purposes except（）
单项选择题 A feedback is an input（）
