GWD 8-34 SLOTH化石的题，HELP!

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.

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

2. 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

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

4. sloth, found in Puerto Rico in 1991, have been dated(为什么用完成时态？) at 34 million years old, making the sloth the earliest known mammal on
5. sloth which, found in Puerto Rico in 1991, was dated at 34 million years old, made the sloth the earliest known mammal of

感觉d的完成时态不对呀，为什么不能选e?还有，C中这个THIS是不能这样指代的对吗？

怎么没人解答，NN，你在哪里？我深情地呼唤你！

首先fossils,所以was就是不对的，E不能选