单项选择题
For an ordinary four-stroke engine the inlet valves open （）
A.after TDC B.before TDC C.after BDC D.before BDC
单项选择题 For an ordinary four-stroke engine the exhaust valves open （）.
单项选择题 For an ordinary four-stroke diesel engine the exhaust valves close （）.
单项选择题 For a main diesel engine the lube oil in the bearings is drawn from （）, usually located in the bedplate.
