When drive-ins were at the height of their popularity in the late 1950’s, 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
I choose option B over C.
A) "Less" cannot be used here, it is used for uncountables i.e water
D) Which number (number 1 or 2 or 3 or 4..) is less ...
E) "It" is singular and cannot be used here.
Between B and C, i will go with B because of the word "that" in C.