离心泵汽蚀破坏主要发生在()。
A.叶片进口背面靠前盖板处
B.叶片进口正面靠前盖板处
C.A或B
D.叶轮外缘叶片及盖板、蜗壳或导轮处
参考答案:D
— How wonderfully you are playing the piano! do you practice it a week?
— Twice. Practice makes perfect.
A. How often B. How many times C. How soon
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