单项选择题
When the direction handle of telegraph is moved, the relative position of camshaft and crankshaft will be（）
A.changed accordingly B.unchanged C.positioned ahead D.positioned astern
单项选择题 Which one of the followings may not be checked before engine starting?（）
单项选择题 The is employed to warm up a large diesel engine before its starting（）
单项选择题 In slow speed two-stroke engines,（）the fresh air entering begins when and stops as（）
