单项选择题
Auxiliary boilers are divided into several classifications, one of which is （）.
A.water-tube supercritical circulation B.water-tube forced circulation C.fire-tube controlled circulation D.fire-tube express circulation
单项选择题 Load control on a diesel engine is accomplished by （）.
单项选择题 When reassembling the bowl of a disk-type centrifuge, the bowl or locking ring is rotated （）.
单项选择题 In diesel engines designed with a crosshead, the motion of the piston rod can be described as （）.
