122.And scores of online discussion boards have popped up on which people discuss negative experiences tied to too much time on the Web.

英语四级译文:
网上突然出现了很多讨论区，专门讨论花太多时间上网的负面体验。

四级词汇讲解:
本句的主干是boards have popped up。on which引导的是以online discussion boards为先行词的定语从句，起补充说明作用，其中过去分词短语tied to too much time on the Web作negative experiences的后置定语，tied与negative experiences为被动关系。
pop up的意思是“突然出现，冒出来”。如:

After the rain, mushrooms seem to pop up overnight.
下过雨后，蘑菇似乎一夜之间就冒了出来。
tie...to...的意思是“使紧密结合”。如:
Our success is tied to you.我们是否成功和你紧密相关。

英语四级考点归纳:
过去分词短语作定语时，通常放在所修饰的词之后，实际上相当于一个定语从句。如:
※ These are problems left over by history.=These are problems thatlwhich axe left over by history.这些是历史遗留下来的问题。
※ I like the idea presented by my dad.=I like the idea that/which is presented by my dad.我喜欢爸爸提出的主意。
※ She is the first nurse trained by their country.=She is the first nurse that/who is trained by their country.她是她们国家自己培养的首位护士。