rush hour与rush hours的区别

题目

rush hour与rush hours的区别
beijing has so many buses that there is often a taffic jam in rush hours,请问为什么用rush hours而不用rush hour（我知道他们都有交通拥挤高峰期的意思）?
希望知识帝能作出详细回答,感激不尽

答案

rush hour是指交通拥挤高峰期
而rush hours是指“每次”交通拥挤高峰期
另一个例子是Sunday和Sundays
Sunday是周日的意思
而Sundays是指“每个周日(every Sunday)”的意思
e.g.I play tennis on Sundays.(即是我每个周日都去打网球的意思)