You should be careful of such a personflatters you in your presence and speaks ill of you

问题补充：

You should be careful of such a personflatters you in your presence and speaks ill of you in behind.

A. who

B. that

C. as

D. which

答案：

A. who

B. that

(答案→)C. as

D. which

解析：考查定语从句。such … as …如此……以致……，as在从句中作主语，选C。