All native american Indians in south Carolina are classified as eastern woodland Indians because of ... a. similar tribal alliances b. languages c. access to natural resources d. both a and b

The Eastern Woodland Region, and even South Carolina are distinguished by a great variety of Indigenous families from many language families. So b) and d) have to be both wrong.

Similarly because of the vastness of the Eastern Woodlands, similar alliances among all of them were difficult.

On the other hand the answer c) is correct: the Eastern Woodlands have similar natural resources, resulting in a similar lifestyle of those living there.