一、that 作限定词或代词
that可以作限定词或代词连接名词或名词短语，也可单独使用，用以指代人或者物。此外，that不仅可以指代单独的人或物，还可以指代一句话。
例：Furthermore, in the early days of long line fishing, a lot of fish were lost to sharks after they had been hooked. That is no longer a problem, because there are fewer sharks around now. [2006, text3]
分析：
A.分析句子结构。Furthermore, in the early days of long line fishing, a lot of fish were lost to sharks //after they had been hooked. That is no longer a problem, //because there are fewer sharks around now.
第一个句子的主句为a lot of fish were lost to sharks，介词短语in the early days of long line fishing作状语，after引导时间状语从句。第二个句子主句是That is no longer a problem, that为代词，because引导原因状语从句。
B.分析that指代。that指代第一句话，“a lot of fish were lost to sharks after they had been hooked”，其中after引导时间状语从句。
C.译文：而且，在使用多钩长线捕鱼的初期，许多鱼被钩住后又被鲨鱼夺走。这不再是一个问题，因为附近的鲨鱼更少了。
二、that作副词表示程度，相当于so
例：It isn’t all that cold. 天没有那么冷。
三、that作连词引导各类从句
(一)that引导名词性从句
that后面连接一个完整的陈述句，可以位于主语、宾语、表语或同位语的位置，分别引导主语从句、宾语从句、表语从句和同位语从句。此时，that没有实意，而且不在从句中做任何成分。that引导主语从句和同位语从句时不可以省略。
例1：That the plates are moving is now beyond dispute. (主语从句)
地球板块是在漂移的，这一事实毋庸置疑。
例2：The truth is that everyone should take care of orphan, not just the authorities.(表语从句)
事实是，所有人都应该照顾孤儿，而不仅仅是完全由政府承担。
例3：All people believed that it was right to rescue the temple. (宾语从句)(注：that可以省略)
所有人都认为拯救古庙是正确的。
例4：The students expressed their hope that they could be admitted by that university.(同位语从句)
学生们表达了他们向被这所大学录取的愿望。
(二)that引导定语从句
that引导定语从句，在从句中充当主语、表语或者宾语，既可以指代人，也可以指代物。that在定语从句中作宾语时，引导词that可以省略。
例1：The professor that you admire most will visit our university next month.
你敬仰的那个教授下月会到我们学校参观。
例2：This is one of the subways that will be put into use in two years.
这是未来两年内将开通的地铁之一。
例3：I have nothing that is worth reading.
我没有什么值得一读的东西。
(注：当先行词中有不定代词、形容词最高级、序数词或者先行词被the only，the very等限定词修饰等情况下，定语从句引导词也只能用that。)
(三)that与其他单词结合引导状语从句
that可以和其他单词结构共同引导状语从句，例如such...that，so...that等引导结果状语从句，in order that，so that等引导目的状语从句，in that，now that，on the grounds that等引导原因状语从句，suppose/supposing/assume/assuming/provided/providing that，on condition that等引导条件状语从句等。
例1：She has made such rapid progress that before long she could pass the exam.
她进步很快，不久就能通过考试的。
例2：You should make full use of this opportunity so that you can get rich experience.
你应该充分利用这次机会，以便获得丰富的经验。
例3：Supposing that you were in my position, what would you do?
如果你在我的位置，你会怎么做?
例4：On condition that you were lost in the desert, you should ask for help as soon as possible.
如果你在沙漠中迷路，你应该尽早寻求帮助。
(四)that引导强调句
“It is/was+被强调部分+that从句”是高频使用的一种强调句型，其中被强调部分可以作从句的主语、宾语和状语等。强调句中去掉“it is/was”和“that”后，句子成分和语义仍然完整。
例：It was after the war was over that Einstein was able to come back to his research work again.
战争结束后爱因斯坦才能重新进行他的研究工作。
