化工厂所应用离心泵，按叶轮数目可分（）和（）。
参考答案：单级离心泵；多级离心泵
两个数位间的进率都是十。[ ]
We often forget to enjoy the simplest things in our life such as flowers, trees, fresh air, walking with friends
and family, or _____ have a good time. [ ]
A. in the end
B. after all
C. in other words
D. at the same time
