1.That a nation should protect

1.That a nation should protect its cultural heritage is very essential.
2.It is very essential that a nation should protect its cultural heritage.
3.It is very essential for a country to protect its cultural heritage.
4.A pressing issue is that a nation should protect its cultural heritage.
5.The majority of people think that a nation should protect its cultural heritage.
6.The majority of people take the view that a nation should protect its cultural heritage.
请问老师，这些句子都是什么从句？尤其是第一个，这令人难以捉摸啊！第三个句子算不算从句？第四个从句是主语从句还是宾语从句？