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 so, as
D. more, than
答案：
A. as, as
B. so, as
(答案→)C. not so, as
D. more, than
解析：as...as意为和……一样，表示同级的比较。使用时要注意第一个as为副词，第二个as为连词。其基本结构为：as+ adj./ adv. +as。其否定式为not as/so +adj./ adv. +as。例如： This dictionary is not as/so useful as you think.这本字典不如你想象的那样有用。 根据语境可知此题选择C。
