When drive-ins were at the height of their popularity

[LongyingZ41]

When drive-ins were at the height of their popularity in the late 1950s, some 4,000 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. there 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

Is B the correct ans? I am confused about the description "as many". Can you help explain?
I think CDE are wrong because amount cannot modify countable nouns, am I right?
Thank you very much!

[RonPurewal]

please search the forum before posting. thank you.

when-drive-ins-were-at-the-height-of-their-popularity-in-the-t6550.html