The gyrfalcon, an Arctic bird of prey, has survived a close brush with extinction; its numbers are now five times greater than when the use of DDT was sharply restricted in the early 1970's.

A. extinction; its numbers are now five times greater than

B. extinction; its numbers are now five times more than

C. extinction; their numbers now fivefold what they are

D. extinction; now with fivefold the numbers they had

E. extinction; now with numbers five times greater than

I picked B. But the answer is A. I thought "more than" is used for countable nouns and "greater than" for uncountable. Help Please!