液压缸的作用是什么,有哪些类型?
参考答案:
液压缸是液压系统中的执行元件,是一种把液体的压力能转换成机械能以实现直线往复运动的能量转换装置。主要有:活塞缸、柱塞缸两类。
—Korean singer Jang Nara ______ China for years.
—Last week, she also ______ her wish to learn cross-talk.
A. has been in; expressed
B. has gone to; expressed
C. has been to; has expressed
D. has been in; has expressed
钻开油气层(目的层)前,试压间隔已经超过()天。全套井控设备应进行试压检查。
A.10
B.20
C.30
D.100