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.