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.

The rising of the exhaust temperature in manifold pipe ...

单项选择题The rising of the exhaust temperature in manifold pipe may NOT result from （）.

The rim of the piston may contain cut-out portions to a...

单项选择题The rim of the piston may contain cut-out portions to accommodate （） when they open.

The removal of （） from lubricating oil will reduce engi...

单项选择题The removal of （） from lubricating oil will reduce engine wear and possible breakdowns.