单项选择题 When the order （） is received from the bridge, the main air stop valve in the starting air line should be shut.

单项选择题 When the follower is on the base circle of the cam, the pump plunger is at the （） of its stroke.

单项选择题 When a crankshaft has to be handled outside the engine, it should be carefully supported in a manner which will avoid （） high bending moments on it.