单项选择题
A.up and down；reciprocating
B.up and down；rotating
C.back and forth；reciprocating
D.back and forth；rotating
单项选择题 The connecting rob is fitted between the crosshead and the crankshaftIt transmits the firing force, and together with the crankshaft convert the （） motion to a （） motion.
单项选择题 The （） of the semi-built method of the construction crankshaft is that by making the two webs and crankpin from a single forging the grain flow in the steel follows the web round into the crankpin and back down the other web.
单项选择题 Today, crankshafts for large 2-stroke crosshead engines are of the （）type.