问题补充：
-----The classroom is clean it was yesterday.
------Sorry, I forgot to clean it.
A. as, as
B. so, as
C. not as, as
D. more, than
答案：
A. as, as
B. so, as
(答案→)C. not as, as
D. more, than
解析：句意：----教室没有和昨天一样干净。----对不起，我忘记打扫了。not so/as…as…和……不一样……clean的比较级是cleaner,根据题意，故选C
