单项选择题
Among the main propulsion units on board the ship with the same capacity, the lightest one is（）.
A.steam engine B.steam turbine C.gas turbine D.diesel engine
单项选择题 The rotating range of the low speed diesel engine is usually lower than （）.
单项选择题 Before using or operating any equipment, you should first （） its manual thoroughly and understand its contents（）.
单项选择题 When we say that two objects have relative motion, we mean （）.
