1.連詞that, if, whether，連接代詞what, which, who, whom, whose以及連接副詞how, when, why, where可用來引導(dǎo)名詞從句，充當(dāng)主語、表語、賓語等。非正式文體中的賓語從句常省略that。例如
I think (that) he’ll be back in an hour. 我認(rèn)為他一小時(shí)后就會(huì)回來。
Who they are doesn’t matter much. 他們是誰沒什么大關(guān)系。
He asked me if/whether I knew John. 他問我是否認(rèn)識(shí)約翰。
此外，that, which, who, whom, whose, when, why, where等還可以引導(dǎo)定語從句。
2.連詞when, while, before, after, till/until, since, as soon as等引導(dǎo)時(shí)間狀語從句。例：
She said hello to me when she saw me. 她看到我的時(shí)候，和我打了招呼。
I’ll wait here until you come back. 我將在這里等你回來。
3.連詞if, unless引導(dǎo)條件狀語從句;because, as, since引導(dǎo)原因狀語從句。例如：
I’ll help her if she asks me to. 如果她要求我，我就幫助她。
I won’t help her unless she asks me to. 除非她要求我，否則我不會(huì)幫她。
He didn’t come because he was ill. 因?yàn)樗×�，所以沒來。
As he hasn’t appeared yet, we shall start without him. 既然他還沒有出現(xiàn)，我們就先開始吧。 Since everybody is here, let’s begin. 既然大家都到了，咱們就開始吧。
4.連詞in order than, so that引導(dǎo)目的狀語從句;so…that…引導(dǎo)結(jié)果狀語從句。例如：
I locked the door in order that we might continue our discussions undisturbed. (=I locked the door in order to continue our discussions undisturbed.) 我把門鎖上了，以便我們可以繼續(xù)討論而不受打擾。
The car ran so fast that I couldn’t see who was in it. 汽車跑得那么快，我沒看清誰坐在里面。 5.連詞than, as…as…, not as/so…as…用來引導(dǎo)比較狀語從句。例如：
He is better educated than his pother. 他比他兄弟受的教育好。
He is as well educated as his pother. 他和他兄弟受的教育一樣好。
He is not as/so well educated as his pother. 他沒有他兄弟受的教育好。
6.連詞although, though 引導(dǎo)讓步狀語從句;where, wherever 引導(dǎo)地點(diǎn)狀語從句。例如：
I’ll go wherever you go. 不管你去哪兒，我就去那兒。
Stay where you are! 原地別動(dòng)!
Though/Although she is rich, she’s not happy. 盡管她富有，但她并不幸福。
一般來說，連詞性質(zhì)的連接詞連接兩個(gè)分句或引導(dǎo)一個(gè)從句醫(yī).學(xué).全.在.線52667788.cn，兩個(gè)分句或主從復(fù)合句之間用逗號(hào)連接。
(三)副詞性連接詞
副詞性質(zhì)的連接詞不能象連詞一樣分句或主從復(fù)合句之間用逗號(hào)連接。也就是說它們不能連接兩個(gè)分句或引導(dǎo)從句。它們引導(dǎo)的句子與前面的句子之間要用分號(hào)或句號(hào)，而它們與引導(dǎo)的句子之間往往用逗號(hào)。副詞性質(zhì)的連接詞在寫作中常常使用，主要分為以下幾類：
1.表示順序的，如first, in the first place, then, finally, in the end等等。尤其要注意then. 如： 誤：He graduated from college in 2003, then he found a job.
正：He graduated from college in 2003, and then he found a job.或者He graduated from college in 2003. Then he found a job.
2.表示遞進(jìn)關(guān)系的，如in addition, what is more, furthermore, moreover等。注意in addition 與in addition to 的區(qū)別：in addition 是副詞性質(zhì);而in addition to 是介詞性質(zhì)，后面必須接賓語。
3.表示轉(zhuǎn)折關(guān)系的，如 however, nevertheless, nonetheless, on the contrary, in contrast, 等等。要注意不要把however 當(dāng)成連詞。如：
誤：In 2003, the United States launched the war on Iraq on account of Iraq possessing weapons of mass destruction (WMD), however, no WMD has been found in Iraq so far.
正：In 2003, the United States launched the war on Iraq on account of Iraq possessing weapons of mass destruction (WMD). However, no WMD has been found in Iraq so far.
