单项选择题
For an ordinary modem marine four-stroke engine the inlet valves close （）.
A.after TDC B.before TDC C.after BDC D.before BDC
单项选择题 For an ordinary four-stroke engine the inlet valves open （）
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 （）.
