Fossils of the arm of a sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of the Greater Antilles islands.

A.   sloth found in Puerto Rico in 1991, and dated at 34 million years old, made it the earliest known mammal of

B.   sloth, that they found in Puerto Rico in 1991, has been dated at 34 million years old, thus making it the earliest mammal known on

C.   sloth that was found in Puerto Rico in 1991, was dated at 34 million years old, making this the earliest known mammal of

D.   sloth, found in Puerto Rico in 1991, have been dated at 34 million years old, making the sloth the earliest known mammal on

E.    sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of

 我选Ｄ了，但是答案怎么有Ｄ版还有Ｃ版，还各自讲的很有道理，到底是哪个呢？请ＮＮ指点一下．．．

C 中THIS应该指代SLOTH. 不知道是否正确?

D 中HAVE BEEN DATED 感觉时态错.