GWD-8-41

When drive-ins were at the height of their popularity in the late 1950's, some 4000 existed in the United States, but today there are less than one-quarter that many.

A. there are less than one-quarter that many

B. there are fewer than one-quarter as many

C. ther are fewer than one-quarter of that amount

D. the number is less than one-quarter the amount

E. it is less than one-quarter of that amount

the correct answer is C.

但是4000 (drive-ins) 这么和 that amount 对起来? 应该是number 才对吧?

amount通常都是修饰不可数名词的.

这道题答案是C吗？