单项选择题
Crankshafts of medium speed engines are （） from a single piece of steel.
A.unusually solid welded B.never be solid forged C.almost invariably solid forged D.almost invariably be welded
单项选择题 Cracks in the cylinders and cylinder covers may （） unequal heating.
单项选择题 Cracks in cylinder and cylinder covers may （） from unequal heating.
单项选择题 Cooling of engine is achieved by circulation a cooling liquid around internal passages within the （）.
