Why is it that some nations have disappeared altogether?请问这个句子是什么结构?

Why is it that some nations have disappeared altogether?请问这个句子是什么结构? that's what it is there for.原句是 Why don’t you get some help from the graduate assistance.That’s what it is there for. That is why,This is why,It is why的区别 That is why some countries have whaled for commercial pruposes. 句子解析 why is it some nations have disappeard altogether A： Why is it that some people are always buying beyond their means? I mean, they do not make that 要翻译!要快!我急用 what i do not know is that why...是不是应该改为is it that why啊 可不可以这样说It is that why...或者It is why ... That's why it is called:The Present是什么意思? that is why it's called the present. it is no wonder 后用why还是that? why do you think that it is true? why is that you donn't care about it? 英语翻译Why are you so sure that it is a It is why…和That is why… 的区别（说明+例子） why it is 还是why is it So why is that why is that?