8.Watching the sun rise above the branches of trees whose roots stretch deep into the heart of the Wall ,you feel you ar

8.Watching the sun rise above the branches of trees whose roots stretch deep into the heart of the Wall ,you feel you are standing on a man-made structure that has indeed become part of ___.
A.the nature B.nature C.a nature D.natures
为什么不是其它选项?尤其是A