The water flows at about 1.5 metres per second.

　　水的流速約為每秒1.5米。

　　The population is increasing at about 6% per year.

　　人口以每年約6%的速度增加。

　　We restrict the number of students per class to 10.

　　我們將每個班的學生人數(shù)限定為10人。