单级双吸离心泵的（）和泵体的连接缝是水平中开的，所以又称为水平中开式泵。
A、水封环
B、泵轴
C、填料函
D、泵盖
参考答案：D
写出下面各数．
八亿八千五百万六千五百
写作：______
三千零八亿零九千
四十二亿零九十万零五
五十三亿零七万三千
六百四十亿七千三百万零五
写作：______．
There are fifty ______ and ______ in our school. [ ]
A. woman teachers; girl students
B. women teachers; girls students
C. women teachers; girl students
D. women teacher; girls student
