Not C?

I find the language between (A) and (C) to be quite similar - the only thing I can think of is that the argument requires the people using the computers to spend more money - which is discussed in (A) but not explicitly in (C)?

C is different from A because C says these consumers would spend little to no money on purchases from the advertisers, but A says only that they now spend more. We don't know what the consumers would have spent before - maybe they frequented this company already? - but we do know from "increased sales" that they do now sell more. Therefore, A is the best answer.

Thank you!