一、用于引導(dǎo)名詞性從句的引導(dǎo)詞有以下幾類(lèi)：
連接代詞： what, which, who, whom, whose
連接副詞： when, where, why, how
連接連詞： that （賓語(yǔ)從句或表語(yǔ)從句中"that"有時(shí)可以省略）；whether,if （均表示“是否”表明從句內(nèi)容的不確定性）；as if ,as though （均表示“好像”，“似乎”）

二、what, which在從句中作主語(yǔ)、賓語(yǔ)、表語(yǔ)或定語(yǔ)；who在從句中作主語(yǔ)、表語(yǔ)；whom在從句中作賓語(yǔ)；whose在從句中作定語(yǔ)；when, where, why, how在從句中分別作時(shí)間狀語(yǔ)、地點(diǎn)狀語(yǔ)、原因狀語(yǔ)、方式狀語(yǔ)。例如
1.Choose which you like best.
選你最喜歡的。
2.Who has taken away my bag is unknown.
誰(shuí)拿走了我的包還不知道。
3.Have you decided whom you are to nominate as your candidate?
你們是否已經(jīng)決定提名誰(shuí)做候選人了?
4.He asked when Mr. Gilbert would be allowed to go home.
他問(wèn)什么時(shí)候可以允許吉爾伯特先生回家。
5.Where we can look up his address is still a problem.
我們?cè)谀膬嚎梢圆榈剿牡刂愤€是個(gè)難題。
6.Why he did that wasn’t quite clear.
他為什么做那件事還不十分清楚。
7.How they will solve the serious problem has not been decided.
他們將怎樣解決這個(gè)嚴(yán)重問(wèn)題還沒(méi)有決定。

三、what作連接代詞引導(dǎo)的名詞性從句既可以表示一個(gè)問(wèn)“什么……？”的問(wèn)題， 也可以表示相當(dāng)于“名詞/代詞＋關(guān)系代詞引導(dǎo)的定語(yǔ)從句”結(jié)構(gòu)的意思， 這種特殊用法在語(yǔ)法上被稱(chēng)作“關(guān)系代詞型的what”，例如：
1. He is not what (=the person that) he was a few years ago.
他不是幾年前的他了。
2. This is what (=the place that) they call Salt Lake City.
這就是他們稱(chēng)作鹽湖城的地方。
3. What (=the place that) is now the North Sahara Desert was once a civilized world. 現(xiàn)在的北部撒哈拉沙漠曾是一個(gè)文明世界。
4.Our income is now double what (=the income that) it was ten years ago.
我們現(xiàn)在的收入是十年前的兩倍。
5.The color of the flower is different from what (=the color that) it was in the morning.
花朵(現(xiàn)在的)顏色與它早上的顏色不同。
6.How did the cheats explain the fact that the Emperor didn't feel the new clothes in him?
皇帝覺(jué)得身上并沒(méi)有穿上新衣，對(duì)這個(gè)問(wèn)題騙子是怎樣解釋的?
7.I owe it to you that I am still alive.
幸虧你，我現(xiàn)在還活著。
8.She made a request that the doctor(should)be sent for at once.
她請(qǐng)求立即請(qǐng)醫(yī)生來(lái)。
9.You must see to it that the children don't catch cold.(=You must see to it,and It is that the children don't catch cold.）
你要當(dāng)心，別讓孩子們著涼了。
10.She told me that she would accept my invitation.
她告訴我，她接受我的邀請(qǐng)。