注意：what不可以用在定語(yǔ)從句中.
定語(yǔ)從句的關(guān)系代詞 that的用法:若先行詞指人或物則代替先行詞在定語(yǔ)從句中充當(dāng)主語(yǔ)或賓語(yǔ)
The animal that \which is lost is a panda.
先行詞 指物代替先行詞在定語(yǔ)從句中充當(dāng)主語(yǔ)
She is the person that \who we are worried about.
先行詞 指人代替先行詞在定語(yǔ)從句中充當(dāng)賓語(yǔ)
which引導(dǎo)的定語(yǔ)從句的用法
which可以引導(dǎo)定語(yǔ)從句,修飾表示事物的先行詞,在定語(yǔ)從句中充當(dāng)主語(yǔ)、賓語(yǔ)或者表語(yǔ).例如：He was reading a book,which was about war.他正在讀一本關(guān)于戰(zhàn)爭(zhēng)的書.（關(guān)系代詞which在修飾book的定語(yǔ)從句中充當(dāng)主語(yǔ).）
He was reading a book,which he had bought from London.他正在讀一本書,這本書是從倫敦買回來(lái)的.（關(guān)系代詞which在修飾book的定語(yǔ)從句中充當(dāng)賓語(yǔ).）
which引導(dǎo)非限定性定語(yǔ)從句時(shí)有一個(gè)特殊用法,即它所引導(dǎo)的非限定性定語(yǔ)從句修飾主句中更多的部分甚至整個(gè)主句（這時(shí)被定語(yǔ)從句所修飾的“先行詞”要作廣義理解）,which仍在定語(yǔ)從句中作主語(yǔ)、賓語(yǔ)或表語(yǔ).例如：
He set free the birds happily,which was a celebration for his success.他開心地把鳥放了,這是對(duì)他成功的一種慶祝.
把非限定性定語(yǔ)從句“which was a celebration for his success”的先行詞視為主句中的“the birds”顯然不符合整句的語(yǔ)境,被“which was a celebration for his success”所修飾的是整個(gè)主句,which所引導(dǎo)的這類特殊的非限定性定語(yǔ)從句對(duì)主句所敘述的情況進(jìn)行某種意義的補(bǔ)充說(shuō)明,which?？勺g為“這一點(diǎn),這件事”.