Here is some form of explanation I found on
MGMAT:
A) doesn't seem likely. "Only by a comprehensive approach" is not discussed. But, it does seem like it might be related to what is in the argument, which is a somewhat non-comprehensive approach. Let's keep it for now.
(B) is not provable. This has nothing to do with the text.
(C) is not provable. This goes well beyond the text.
(D) is not provable. This also goes well beyond the text.
(E) is not provable. This is much more specific to be provable based on this text.
Le'ts go back to (A), our only viable answer. Could (A) be provable?
What we're told is that a system of payment by separate groups cannot work. Therefore, we know that either:
If a system can work, it's going to be not by separate groups, aka "comprehensive."
or
No system can work at all.
So, the system can only work, if it can work at all, using a comprehensive approach.
(A) is the most provable based on the text, and therefore correct.