[求助]大全122，people是不可数名词，为什么用fewer而不用 less修饰？

DQ122 ：

As a result of the continuing decline in the birth rate, less people will enter the labor force in the 1980’s than did in the 1960’s and 1970’s, a twenty year period during which people born after the war swelled the ranks of workers.

(A) less people will enter the labor force in the 1980’s than   

(B) less people will be entering the labor force in the 1980’s as  

(C) fewer people will enter the labor force in the 1980’s as

(D) fewer people will be entering the labor force in the 1980’s as（E）

(E) fewer people will enter the labor force in the 1980’s than

我的问题是：people是不可数名词，为什么用fewer而不用 less修饰？

恳请赐教！！！

people是可数名词...修饰人要用fewer的

那less 只修饰不可数喽？