Arod made of cobalt with a mass of 0.80 kg is heated to 800°c, then dropped into 6.00 kg of water at 10°c. what is the total change in entropy (in j/k) of the rod-water system, assuming no energy is lost by heat from this system to the surroundings

Ohm's law tells you that i = v/r where v is equivalent voltage and r is equivalent resistance of the circuit
since all circuits have the same voltage, your question is really asking which circuit has the lowest total resistance, since the lower the resistance, the higher the current
circuit a has a resistance of 5 ohms; circuit c is in series so has a resistance of 10 ohms; circuit b is in parallel and therefore has a resistance of 2.5 ohms (review your notes on adding resistances in parallel and series); therefore b has the highest current