请教一道GWD的题

林中雪

GWD-8-Q41:

When drive-ins were at the height of their popularity inthe late 1950’s, some 4,000 existed in the United States, but today thereare less than one-quarter that many.

1. there are less than     one-quarter that many
   

there are fewer     than one-quarter as many

there are fewer     than one-quarter of that amount

the number is less     than one-quarter the amount

it is less than     one-quarter of that amount   答案是C，为什么D不对呢

cidisnotjayz

one-quarter the amount。

littledaniel

应该是B吧，amount是不可数的啊