Hawaii is the only one of all U.S. states that still has a sizable native population, and where this group has a strong chance of remaining.
(A) that still has a sizable native population, and where
(B) that still has a sizable native population, where
(C) that still has a sizable population of natives, and where
(D) where the native population is still sizable;
(E) where there is still a sizable native population and where
I would say C.
A,B,D,E :- 'this group' is not explicit here. This group refers to the native population. The sentence intends to convey two things:-
1) Hawaii has a large native population
2) The native population has a strong chance of survival here.
in A & B the sizeable and native is used to define aspects of population. But in C, this group can be referred back to natives.
Hence I would go for C. It's hard to agree that the group refers to Hawaii. It would be very puzzling if the answer is D