单项选择题
The scavenging air ports are located at （） that they are just exposed by the upper edge of the piston when the piston is in the bottom dead center position.
A.so a height B.such a height C.so high D.such high
单项选择题 The rising of the exhaust temperature in manifold pipe may NOT result from （）.
单项选择题 The rim of the piston may contain cut-out portions to accommodate （） when they open.
单项选择题 The removal of （） from lubricating oil will reduce engine wear and possible breakdowns.
