First of all, I'd like to caution you about accepting answers that contain a ", which" clause. Make certain that the comma which refers to the word or noun phrase immediately preceding the comma. In this case, for example, is the comma which intended to modify the CONCEPT or PERSONAL COMPUTING? It's ambiguous.

Second, answer choice (C) is not parallel. If you're going to use which one one side, you should use which on the other side of the and.

Astute observers may note, however, that (A) doesn't seem that parallel either. Hatched...and permeating... seem, on the face of it, to be incompatible. However, that is not necessarily the case. Both are adjectives and both are modifying the same thing.

Other acceptable constructions that appear, on the surface, to have parallelism problems:

John, born in Paris and living in Marseilles, has discovered...
Bored and yawning, the researcher objected to the length of the meeting.
Lina's sunbird, a four-and-a-half-inch animal found in the Phillipines and resembling a hummingbird...

All of these sentences are actually just fine. If you see a sentence like one of these on your GMAT test, you are doing extremely well on the verbal part.