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) Because Madagascar was one of the last habitable areas of the earth to undergo human settlement, it is
E的时态很别扭,且it指代的是不是十分清楚呢?