单项选择题 In a four-stroke engine the camshaft rotates at （）.

单项选择题 In an engine with air inlet valve and exhaust valve on its cylinder heads the fresh air will enter into the cylinder （） and the gases exhaust （）, there being an adequate overlap between the inlet opening and the exhaust closing.

单项选择题 In an engine with a pot-shaped piston, some lubricating oil from the main bearing will pass along a （） in the crankshaft to the bottom end bearing andthen up a connection rod to the gudgeon pin.