用四舍五入法对数5664935取近似值，保留三个有效数字，结果是______．
5 664 935取近似值，保留三个有效数字，结果是5.66×106．
Maggie _____ watch Beijing Opera rather than _____ pop songs, though she can't understand it. [ ]
A. prefers; listen to
B. prefers to; to listen to
C. prefers; listening to
D. prefers to; listen to
罗茨流量计更换重要元件后，恢复使用前，必须重新（）。
A.启动
B.安装
C.校零位
D.检定
