A) This can easily be eliminated because limited in their usefulness seems to be modifying the entrepreneurs, and thus the sentence does not really makes sense.
B) The sentence created using this choice is somewhat awkward in the beginning part, Based on the limited usefulness thus far. Also the sentence created does not make sense in that believing that something is the start of something very important would not be based on limited usefulness.
C) Once again very important seems to be based on limited usefulness. Also it does not really make sense to say that entrepreneurs believe With the limited usefulness.
D) I still find that this begins awkwardly, but at least it makes sense that the entrepreneurs would believe something to be the start of something very important Despite the limited usefulness thus far. So this choice works.
E) In this choice limited in usefulness seems to be incorrectly modifying entrepreneurs.

This is a funny question. Even the OA, which is D, could be better expressed.

Even so, one can use meaning and modifier logic to hack one's way to the OA, and doing things like that is basically the way to rock GMAT verbal.