单项选择题 When good and steady service conditions have been achieved, the running surfaces of the piston rings and cylinder liner will be（）In addition, the rings will move freely in the grooves and also be well oiled intact, and not unduly worn.

单项选择题 The sealing function of the piston ring is brought about by the gas pressure above and behind the piston ring, which forces it （） against the bottom of the ring groove, and （） against the cylinder wall.

单项选择题 The scavenge port inspection should be carried out（）, to obtain the most reliable result with regard to the effectiveness and sufficiency of the cylinder lubrication and the combustion cycle (complete or incomplete).