ska7945 wrote:The parachutelike membranes of Africa's scaly-tailed flying squirrels differ from those of the flying squirrels in the family Sciuridae because they are attached to a cartilage rod at the elbow instead of the wrist.

(A) because they are attached to a cartilage rod at the elbow instead of
(B) because of being attached to a cartilage rod at the elbow rather than at
(C) in their attachment to a cartilage rod at the elbow instead of being attached at
(D) in that they are attached to a cartilage rod at the elbow rather than at
(E) in their being attached to a cartilage rod at the elbow instead of

This is not a causal relationship. so the use of because is incorrect.. this takes out A and B.
Correct usage is in D "in that".. also rather than is suited here in place of instead of.. becuase of we are talking about preference and not replacement.. hence the answer..
The rule is:
Rather than - shows preference. This expression is generally used in 'parallel' structures.
Instead of - suggests that one person, thing or action replaces another.
There must be other flaws in the other sentences.. but the above three are what took me to choose D.. didn't have to read anymore.

correct answer clearly D