the factory where you visited yesterday is a paper factory改错the factory where you visited yesterday is a paper factorythe factory which you lived ten years ago is a paper factorythere are many stars in the sky which is like the sunthe tallest bay you referred to don't like surfing the internetthe reason that he hasn't come is that he is illthe reason why he told me is that be is illhe  is one of the students who hasn't passed the testwe talked about l

The factory 【where--which/that或去掉where】 you visited yesterday is a paper factory.
因为先行词The factory在定从中作宾语,故用关系代词which/that,
也可把where去掉后不用任何关系代词.
The factory 【which--where】you lived ten years ago is a paper factory.
定从中缺少的是地点状语in the factory,故用where引导定从.
There are many stars in the sky which 【is--are】like the sun.
因为定从中的which指代的是先行词many stars,且在定从中作主语,故用are.
The tallest boy you referred to 【don't--doesn't】like surfing the Internet.
因为句子的主语是The tallest boy,为单三人称,故谓动的助动词用doesn't.
The reason 【that--why】 he hasn't come is that he is ill.
因为先行词The reason 在定从中作原因状语,故定从用why.
The reason 【why--that/which或去掉why】 he told me is that be is ill.
因为先行词The reason 在定从中作told的直接宾语,因此用that/which引导定从或省略不要.
He is one of the students who【hasn't--haven't】passed the test.
因为当先行词为"one of+名词复数"时,定从的谓动由名词复数来决定,故此句中的助动词用haven't.
We talked about lots of people and things 【which--that】 we still remembered that day.
先行词既有人又有物时,定从用that引导.
I have a great number of friends,of【thwm(单词本身也写错了)--whom】most are Americans.
先行词friends指人,且在定从中作介词的宾语时,用whom.
Have you found the pen 【加上with】which you wrote your composition?
先行词the pen在定从中应作介词with的宾语,表示"用钢笔写字":write sth.with the pen.