The yield per acre of coffee berries varies enormously in that a single tree, depending on both its size and on climate and altitude, could produce enough berries to make between one and twelve pounds of dried beans a year.
A. enormously in that a single tree, depending on both its size and on climate and altitude, could produce
B. enormously in that a single tree, dependent on its size and also on climate and altitude, is able to produce
C. enormously, because a single tree, depending on its size and on climate and altitude, is able to produce
D. enormously, because a single tree, being dependent on its size, climate, and altitude, is capable of producing
E. enormously, because a single tree, dependent both on its size as well as on climate and altitude, could produce

1. I know that punctuation is not an important issue evaluated by the GMAT, but I have a doubt with the comma after "because" in choice C. I know that, when a main clause is followed by a subordinate clause, both clauses are not separated by a comma. In other words: Main clause + subordinator + (subordinate clause). Why in this case is there a comma?, or is "because " an exception?, in which cases?
2. Is there a difference between "capable of v-ing" and "able to"?
3. How could we know that we should use "because" instead of "in that"?

OA is C.