15. Madagascar was one of the last habitable areas of the earth to undergo human settlement, which has made it an ideal site for researching rare flora and fauna.
(A) Madagascar was one of the last habitable areas of the earth to undergo human settlement, which has made it
(B) Madagascar was one of the last habitable areas of the earth to have undergone human settlement, and that has made it
(C) Madagascar underwent human settlement as one of the last habitable areas of the earth, which makes it
(D) Madagascar, one of the last habitable areas of the earth, underwent human settlement, making it（E）
(E) Because Madagascar was one of the last habitable areas of the earth to undergo human settlement, it is
请NN帮忙分析一下这道题...我选了D，我觉得同位语感觉挺对的...
还想请教一下，it在什么情况下可以指代前面的整句句子 | 
