[問題]OG11th(ov)-Q72

[stevenyu]

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 number are now five times greater than
(b) extinction; its number are now five times more than

ans:(a)

想請問一下為什麼不能用more…為什麼修飾gyrfalcon就應該用greater
而且為什麼不是用more去修飾number呢…

拜託好心人告訴我…