某离心泵转速为1450RPM，流量为Q，当转速提高至2900RPM时，其流量为（）
A、Q
B、2Q
C、4Q
D、8Q
参考答案：B
填空．
①一本书200页，读了20%，还剩下______页没有读．
②甲数的40%与乙数的50%相等，甲数是120，乙数是______．
—We haven't heard from Jane for a long time.
—What do you suppose ______to her? [ ]
A. was happening
B. to happen
C. has happened
D. having happened
