单项选择题
A.crankshaft
B.connecting rod
C.cross-head
D.main beating
单项选择题 The piston cooling system may employ similar components, except that a drain tank is used instead of a head tank That means this system （）.
单项选择题 The piston cooling system may employ similar components, except that （） is used instead of a head tank.
单项选择题 The pistons are cooled by oil supplied from the forced （） system.