IMO correct option A
The question tests parallelism and idiom.
Correct idiom => as X as Y
Not considering the marked portion in the main sentence maxes X = individuals make hand motions & Y = sighted people do
In A this is parallel.
Research has shown that when speaking, individuals [strike]who
have been blind from birth and have thus never seen anyone gesture nonetheless[/strike] make hand motions just as frequently and in the same way as sighted people do, and that they will gesture even when conversing with another blind person.
A) have thus never seen anyone gesture nonetheless make hand motions just
as frequently and in the same way
as sighted people do, and that
B) have thus never seen anyone gesture but nonetheless make hand motions just
as frequently and in the same way
that sighted people do, and -
As X that Y is wrong C) have thus never seen anyone gesture,
that they nonetheless make hand motions just as frequently and in the same way as sighted people do, and -
that is not parallel & is unnecessary D) thus they have never seen anyone gesture, but nonetheless they make hand motions just
as frequently and in the same way
that sighted people do, and that -
As X that Y is wrong E) thus they have never seen anyone gesture nonetheless make hand motions just
as frequently and in the same way
that sighted people do, and -
As X that Y is wrong