122.And scores of online discussion boards have popped up on which people discuss negative experiences tied to too much time on the Web.
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。
After the rain, mushrooms seem to pop up overnight.
Our success is tied to you.我们是否成功和你紧密相关。
※ 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。