Sentence Correction

Elk now live almost solely in the Rocky Mountains, which would make it seem that elk are mountain dwellers, while they once ranged over virtually all of the continental United States except for a small strip in the extreme Southwest.

A. Elk now live almost solely in the Rocky Mountains, which would make it seem that elk are mountain dwellers, while

B. The fact that elk now live almost solely in the Rocky Mountains would make it seem that they are mountain dwellers, but

C. It would seem that elk would be mountain dwellers because of their living now solely almost in the Rocky Mountains, but still

D. Now living almost solely in the Rocky Mountains, it would seem that elk were mountain dwellers, although

E. It seems that elk would be mountain dwellers from the fact that they now live solely almost in the Rocky Mountains, since


OA is
A

Please explain the answer and why other options are incorrect...

I am not sure if "OA" is correct.
Because in choice "A" which seems to refer back to "Elk" living in Rocky Mountains and per MGMAT and other grammar rules "Which" when used as pronoun should refer mack to immediate noun.
Moreover "they" in non underlined part refers to Elk which is singular and this error is not corrected in any of the choices.
So I doubt the source of this question ??
Guys any other views ???