离心泵有哪些主要构件？
参考答案：
叶轮、轴承、轴向推力平衡装置、泵的密封装置、泵壳
There was never any time for Kate to feel lonely, _____ she was an only child.[ ]
A. ever since
B. now that
C. even though
D. even as
建设创新型国家，关键在( )。
A．人才B．技术C．对外开放D．体制创新
