以下四个句子分别是什么结构，这四种结构的特点是什么，有什么区别：
1If you have degrees, you can earn more money
2 If you exercise regulary, your heart will be strong
3 If I were Russian, I would speak Russian
4 If I had studied more(but I didn't) , I would have passed English with an A (but I failed)
