单项选择题 If the gas pressure behind the ring is built up too slowly, and thereby exerts an inadequate outward pressureIn such a case, the combustion gas can penetrate between the liner and ring, and violently force the ring inwards, in the grooveWhat result will this type of sudden "shock" loading eventually lead to?（）

单项选择题 Broken piston rings manifest themselves during the scavenge port inspection by（）

单项选择题 If due to thick and hard deposits of carbon, the piston rings cannot move freely in their grooves, dark areas will often appear on the upper part of the cylinder wall (may not be the risible at port inspection)What condition of the piston rings can result in this phenomenon?（）