The correct answer is A. capacitor in parallel with contacts.
A capacitor is a device that stores electrical energy in an electric field. When two electrical contacts are close together, a spark can occur when the electric field between them becomes strong enough. A capacitor can reduce the sparking by providing a path for the current to flow through, which reduces the electric field between the contacts.
Option B is incorrect because a capacitor in series with each contact would not provide a path for the current to flow through, and would therefore not reduce the sparking.
Option C is incorrect because resistance in line would increase the voltage across the contacts, which would increase the electric field between them and make the sparking more likely.
Option D is incorrect because a capacitor in parallel with contacts is the only option that would reduce the sparking.