泵不上压的原因是什么？
参考答案：
①泵内有空气
②泵内有异物
③出口阀坏
④入口管漏气
⑤泵壳裂叶轮坏
I was told that the stadium was well worth ___.
A．to visit
B．to be visited
C．visiting
D．of being visited
《内经》以五音归五行，角音属______，宫音属 ______。
