Original text:

It is a harmless habit, but it litters up her desk to such an extent that every time she opens it, loose bits of paper fall out in every direction.

6 - but it litters up her desk ____ that every time she opens it ...

(a) so far (b) as long as (c) in as much (d) so much

我的答案是(d)，但是课本答案是(c)，有点不太明白

谢谢帮忙