south,the south,southern...如何运用（英语高手进）

south,the south,southern...如何运用（英语高手进）
1.这三者有什么区别,词性分别是什么
2.应该怎么用（尤其是和冠词的搭配方面）
3.以下这四道题
(1) _______ Suez Canal brought________ east and_______ west closer.
A.The…/…/ B.The…the…the C./…the…the D./…/…/
(2) ________ earth goes from______ west to______ east.
A.The…the…the B.An…a…a C./…/…/ D.The…/…/
(3) —Which part of China are you from?
—I am from________ of China.
A.south B.the south C.southern D.the southern
(4) I remember he lives in_________ south,so we shouldn’t be walking _________ west.
A./…/ B./…the C.the…the D.the…/
（Key:D D B D,请问为什么这样选）