控制装置的功用是()。
A、预先制备与储存足量的液压油
B、控制液压油流向
C、使防喷器迅速开关
D、实现软关井
参考答案:A, B, C
保留溶液的时间为
A.10~20min
B.30min
C.5~10min
D.20min左右
E.1h
89. His term papers mainly _____ the history of social developments in Song dynasty.
A.does with
B.treats
C.deals with
D.Deals