livemocha. com is a free site visitors can not just learn languages but also chat online.

问题补充：

livemocha. com is a free site visitors can not just learn languages but also chat online.

A. that

B. where

C. which

D. what

答案：

A. that

(答案→)B. where

C. which

D. what

解析：考查定语从句。本题定语从句的先行词是a free site，定语从句的句子结构很完整，故使用关系副词where。句意：livemocha. Com是一个免费的网站，在这个网站里来访者不仅仅可以学习语言还可以在线聊天。故B正确。