Can you please explain why were would make the comparision right?
Correct idiom: X were
......longer than....Y were
Only D employs this correct construction (In isolation is weird)
For A, B, and E, "sub-species were
isolated longer than their marsh cousins" is weird as it seems to be comparing "isolated longer" to "march cousins/sub-species"
We stayed longer in Hawaii than you did - Correct!
We stayed longer in Hawaii than you - Wrong!
Also, here is a little tip.
Whenever you see comparisons in sentences, always make sure that the 'subjects', 'verbs' match up with what is stated previously.
The correct choice here reads:
The woodland sub-species were
isolated from contact with humans longer than were
either their marsh cousins or the tree-dwelling sub-species
Hope it makes sense
Don't be afraid to take a flying leap of faith.. If you risk nothing, than you gain nothing...