Question

--- The classroom is______clean______it was yesterday.
--- Sorry, I forgot to clean it.

1. A.
   as; as
2. B.
   so; as
3. C.
   not so; as
4. D.
   more; than

Answer 1

C
根据句意教师忘记打扫应该是不如以前干净，故只能选表示不及的意思，not so
……as可以表示此意，故选C。