亚硝酸钠废水处理:There are less than 50 students in our class.这里为什么不用fewer而用less than呢

There are less than 50 students in our class.这里为什么不用fewer而用less than呢 There are not than ten books left 改错 How far can a man walk with breaks that are less than 1 hour there were no less than eight houses in the area with a space to rent中文意思谢谢 smaller than=less than吗?JJJJJJJ less than a pearl歌词 less than enough 什么意思？ 请问There is / are more than one student.选哪一个 There is going to be less snow in my hometown this winter than last winter.句子中为何不能用fewer? Available memory less than 128MB!!!100122624