单选题Pistons of marine medium speed diesel engines may be made of （） in order to keep the weight down for balancing purpose at high speed.AleadBforged steelCalloy steelDaluminum alloy
单选题
Pistons of marine medium speed diesel engines may be made of （） in order to keep the weight down for balancing purpose at high speed.
A
lead
B
forged steel
C
alloy steel
D
aluminum alloy
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