It' s a pity that there are many teenagers only on-line activity is chatting with their e

问题补充：

It s a pity that there are many teenagers only on-line activity is chatting with their e -pals !

A. who

B. that

C. which

D. whose

答案：

A. who

B. that

C. which

(答案→)D. whose

解析：句意：很遗憾，有很多青少年在网上的活动只是与网友聊天。通过分析句子结构，可知这个句子中包含一个主语从句和一个定语从句。横线之后到句末是一个定语从句，且关系词在定语从句中作定语，故用whose，选D。