From the stimulus, we know that the political advocate believes that we should subsidize political campaigns because it would have two big benefits. For one, politicians would spend less time on fundraising, allowing them to serve the public more. Secondly, it would make it possible to set caps on individual donations, which would make politicians less likely to be working for big donors and not the public.
Recall that we're looking for an answer choice with a principle that would provide a basis for the advocate's argument.
The political advocate's premises provide us with positive consequences for subsidizing political campaigns. The correct answer choice will likely say something to the effect that the positive consequences of publicly subsidizing campaigns are enough to justify that we should implement public subsidization of campaigns.
(A) says, "If complete reliance on private funding of some activity keeps the public from enjoying a benefit that could be provided if public funds were used, such public funds should be provided."
The political advocate states two big benefits of publically funding political campaigns. (A) states that where these benefits exist, public funds should be provided, so this is exactly what we're looking for. Thus, (A) is the correct answer choice.
Does this make sense? Let us know if you have any other questions!