问题补充：
Don’t talk about such things you are not sure about.
A. which
B. that
C. as
D. what
答案：
A. which
B. that
(答案→)C. as
D. what
解析：考查定语从句。本题定语从句的先行词是things，因为前面有such修饰，所以后面的先行词使用as，as指代先行词在句中作为介词about的宾语。就要：不要谈论一些你不确定的事情。本题容易错选B项，形成such…that…如此…以至于…;that引导的是结果状语从句。
