单项选择题
A built-up exhaust valve is one in which （）.
A.the stem and heads are made of different material B.low-alloy steel is used throughout C.a replaceable valve disk is welded to the head D.the self-centering action comes from motion of the valve stem in the guide
单项选择题 If scavenge box should be hot, （）would occur.
单项选择题 If exhaust temperatures are too high, you should check （）.
单项选择题 Defective timing gear in a diesel engine may lead to （）.
