iMyself wrote:
At one time, bison were the most numerous mammal species in North America and they could be seen in massive herds that stretched across the Great Plains.
A. they could be seen in massive herds that stretched
B. they would be seen in massive herds stretching
C. it could be seen in massive herds that stretched
D. it could have been seen in massive herds stretching
E. it would have been seen in massive herds that stretched
Source: McGraw Hill GMAT
Bison is already mentioned as a plural in non underlined
...
![FLO – Therapy at the Club – Pre-Single [iTunes Plus M4A]](http://is1-ssl.mzstatic.com/image/thumb/Music221/v4/a4/11/88/a41188ed-0f2e-e8d5-1163-d59e373cc58c/26UMGIM30046.rgb.jpg/208x208bb.webp)
