what和than 的用法？

Question

our factory is much more productive now.This year's ptoduction is five times __ it was ten years ago
A.what B.that C.than D.as
答案是A，为什么不是C？？？

Answer 1

看仔细了，如果用than后面弄个was干嘛？
This year's ptoduction is five times than the production ten years ago. (这句话一看就对吧，那么than后面的the production不就是it嘛，替换掉后哪里来was？)

由于这句表示数目关系，变下句型that也能用。以下三种可互换，都对：
This year's ptoduction is five times what it was ten years ago.
This year's ptoduction is five times than the production ten years ago.
This year's ptoduction is five times that of ten years ago.