形容詞加that是什麼從句

是主語從句。例如

lt is  good that we are going to play football next Monday.(下週一我們去踢足球太好了。)       這個句子的it從形式看是主語，實際上它只是代替後面that引導的從句，這個從句纔是真正的主語(主語從句)。這是因爲主語從句作主語太長，放在前面顯得頭重腳輕，才用it代替它。

It's+形容詞+that+從句. - ...... 這個屬於主語從句的範疇：

It+be+said/reporeted/believed+that從句 it是形式主語，指代後面的that從句

如：

It's certain that you should leave.

I am glad that you chose to write on this topic.我很高興你選擇了這個話題。

又如：

I am happy（主句） that she will be back（從句）.

類似的同位語從句：

I heard the news that our team had won.我聽到了我們隊贏了的消息。

主句：I heard the news

從句：that our team had won

類似的還有It句型：

It is doubtful that they will put much pressure on companies to boost returns.

值得懷疑的是，它們是否會對企業施加很大壓力以提高回報率。

一般爲主語從句

形容詞後面加that，常用形式有：

①it is important that…重要

②it is impossible that…不可能…

It is impossible that he should go home.

他不可能會回家去。

③it is necessary that…有必要…

It is necessary that I should return it this morning. 

今天早上我就有必要還回去。

④it is advisable that…最好…

It is advisable that everyone should have a map. 

最好每一個人都有一張地圖。

⑤it is essential that…務必…

It is essential that the meeting starts at eight. 

會議務必在8點鐘開始。

⑥it is desirable that…最好…

It is desirable that everything should be ready by five o’clock. 

最好一切在5點前準備就緒。