That可以引导名词性从句，状语从句和强调句。
It was exactly what I needed是表语从句，是"主句+表语从句"构成的主从复合句,其中表语是由"what"引导的是表语从句来充当.这里"it" 作代词,当然"it"也可替代后面的名词从句放在句首作形式主语,但这里却不成。
that名词性从句。
①引导宾语从句。及物动词后的引导词that可省略。
I didn't expect (that) he could win the championship.
The teacher pointed out that Tom was not working hard enough.
② 引导主语从句。通常采用it作形式主语的句型。
That the earth goes around the sun is known to everyone.
（It is known to everyone that the earth goes around the sun.）
③引导表语从句。
The trouble is that we are short of money.
④引导同位语从句。
引导同位语从句的that和引导定语从句的that是不同的。前者只起语法作用，在从句中不作任何成分；而后者在定语从句中作主语、宾语或表语。举例说明：
The news that he resigned from office surprised us.
The idea that he holds is very common nowadays on campus.
扩展资料：
与that 有关的常见重要短语。
1、in that，意为“既然、因为”。
Criticism and self-criticism is necessary in that it helps us correct our mistakes.
2、now that，意为“既然、由于”。
Now that they have taken matters into their hands, the pace of events has quickened.
3、see (to it) that，意为“注意、务必做到、保证”。
We will see to it that she gets home early.
See to it that you are not late again.
4、seeing that，意为“鉴于、由于”。
Seeing that it is 8 o'clock, we'll wait no longer.
Seeing that he was busy with his work, I didn't disturb him.
参考资料：that-百度百科
That可以引导定语从句 、名词性从句 、状语从句 。
that是表语从句。
技巧：判断是什么从句，就是看从句在整个句子中做什么成分，显然是在整个句子“It was exactly
某某”中做was的表语。当然，是what引导从句，在从句中充当宾语成分，为need的宾语。
扩展资料：
1、(引导名词性从句)
He expressed the hope that we would keep in touch with his firm.他表示希望我们与他的公司保持联系。
My idea is that we should act on his suggestion.我的意见是我们应当按照他的建议去办。
That she is still alive is a relief. 她还活着,这是令人感到宽慰的。
2、(引导状语从句,表示原因或理由)因为,由于
We are glad that we have accomplished another arduous task. 我们都感到高兴因为又完成了一项艰巨的任务。
3、(引导状语从句,表示目的或结果)为了,以至于
He is working hard that he can catch up with the class. 他努力用功,以便赶上班上同学。
4、(引导表示愿望,感叹的从句,主句常省略)
ThatI could stay at home today! 今天要是我能呆在家里多好呀!
参考资料：百度百科——that
本回答被网友采纳That是名词性从句，定语从句，都可以用that来引导。
1.(引导名词性从句)He expressed the hope that we would keep in touch with his firm.他表示希望我们与他的公司保持联系。My idea is that we should act on his suggestion.我的意见是我们应当按照他的建议去办。That she is still alive is a relief. 她还活着,这是令人感到宽慰的。
2.(引导状语从句,表示原因或理由)因为,由于We are glad that we have accomplished another arduous task. 我们都感到高兴因为又完成了一项艰巨的任务。
3.(引导状语从句,表示目的或结果)为了,以至于He is working hard that he can catch up with the class. 他努力用功,以便赶上班上同学。
4.(引导表示愿望,感叹的从句,主句常省略)ThatI could stay at home today! 今天要是我能呆在家里多好呀!
拓展资料
that是一个英文单词，读音是英音[ðət]，美音是[ðæt]，在英语中使用广泛，可用作形容词、代词、连词、副词，还可用于固定搭配。
本回答被网友采纳就是用that引导的从句，名词性从句，定语从句都可以用that来引导。
It was exactly what I needed是表语从句，是"主句+表语从句"构成的主从复合句,其中表语是由"what"引导的是表语从句来充当.这里"it" 作代词,当然"it"也可替代后面的名词从句放在句首作形式主语,但这里却不成.因为"exactly"是副词.如果"it"替代后面的从句做了形式主语,那主句就缺表语成分.。exactly修饰what I needed，it 是形式主语，真正的主语是what I needed。但此句可以是"what I needed was it exactly.”翻译为“这正是我需要的。”
拓展资料：从句由that引导用法
that引导的主语从句that引导的主语从句既可以放在句首也可以放在句末，在实际应用中我们常常采用it形式主语的形式；
that引导的宾语从句that常用来引导宾语从句，通常that可以省略。
例句：He has told me that he will go to Shanghai tomorrow. 他已经告诉我他明天要去上海；
宾语从句的引导词除that 之外,还可以由连接代词(what ,which, who)和连接副词(when, where, how) 等来引导.例如:Do you know what he has said；
that引导的表语从句基本结构：主语 + 系动词 + that从句。例句：The fact is that we have lost the game.事实是我们已经输了这场比赛；
同位语从句通常由that引导，例句The news that we won the game is exciting.我们赢得这场比赛的消息令人激动；
用that引导定语从句的情况，在不定代词，如：anything, nothing, something, the one, all, much, few, any, little等作先行词时，只用that，不用which；例句：There is nothing that we can use.这里没什么我们可用的东西。
That可以引导定语从句 、名词性从句 、状语从句 。
1、用作关系代词，引导定语从句。
The only thing that I can do is to have a rest . 我唯一能做的事就是休息。
2、用作关联词，引导名词性从句。
That the earth turns around the sun is known to all. 地球围着太阳转这一点是众所周知的。（引导主语从句）
It so happens that I know the man. 碰巧我认识那人。（主语从句）
I will see to it that everything is ready. 我会注意把一切准备妥当的。(宾语从句) The trouble is that we are short of money.困难就在于我们缺钱。（表语从句）
There is no doubt that he is the best choice for this position. 无疑，他是这一职位的最佳人选。（同位语从句）
3、构成短语，引导状语从句。
Bring it nearer so that I may see it better .拿近一点，好让我看清楚些。 ( so that 引导目的状语从句)
She got up early , so that she caught the early bus. 她起的早，所以赶上了早班车。( so that 引导结果状语从句)
In order that everybody should hear him , he spoke loudly. 他大声说话，为了使大家都能听得见。（in order that引导目的状语从句）
Now that they have taken matters into their hands the pace of events has quickened.他们既然已着手自己来处理问题，事态的进展也就加快了。（now that 引导原因状语从句）