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

英語四級譯文:
網上突然出現了很多討論區，專門討論花太多時間上網的負面體驗。

四級詞匯講解:
本句的主干是boards have popped up。on which引導的是以online discussion boards為先行詞的定語從句，起補充說明作用，其中過去分詞短語tied to too much time on the Web作negative experiences的后置定語，tied與negative experiences為被動關系。
pop up的意思是“突然出現，冒出來”。如:

After the rain, mushrooms seem to pop up overnight.
下過雨后，蘑菇似乎一夜之間就冒了出來。
tie...to...的意思是“使緊密結合”。如:
Our success is tied to you.我們是否成功和你緊密相關。

英語四級考點歸納:
過去分詞短語作定語時，通常放在所修飾的詞之后，實際上相當于一個定語從句。如:
※ These are problems left over by history.=These are problems thatlwhich axe left over by history.這些是歷史遺留下來的問題。
※ I like the idea presented by my dad.=I like the idea that/which is presented by my dad.我喜歡爸爸提出的主意。
※ She is the first nurse trained by their country.=She is the first nurse that/who is trained by their country.她是她們國家自己培養的首位護士。