▲表示“……（比）率”，rate 后面通常是接介词 of。如：

What’s the rate of exchange against the dollar?  美元的兑换率是多少？

The rate of inflation has now reached double figures.  通货膨胀率已经达到两位数。

You could earn a higher rate of interest elsewhere.  你在别处可以获得更高的利率。

There is a high rate of juvenile delinquency in this area. 该地区的青少年犯罪率很高。

The rate of growth varies considerably between different industries. 不同产业的增长率有着相当大的差异。

▲但是如果后面是复数名词，则可以用介词 among，表示“在……当中的比率”。如：

There is a low survival rate among babies born before 22 weeks. 少于22 周的婴儿存活率很低。

TheUKhas the highest birth rate among 15 to 19-year-olds in Western Europe.  在西欧，英国女性在15到19岁之间生育率最高。

The suicide rate among men between the ages of 16 and 25 has risen alarmingly. 16至25岁之间男性的自杀率攀升速度惊人。