What is a characteristic of all fuel cells? energy from the sun is converted into electricity. electrical energy is produced from oxidation reactions. oxidation reactions are used to produce thermal energy. a constant source of energy is not required.

All fuel cells have this distinct characteristics: Electrical energy is produced from oxidation reactions. All fuel cells have anodes and cathodes. At the cathode of the fuel cell, hydrogen atoms tend to lose electrons, while at the anode, the hydrogen loses electrons. The overall reaction that happens in a fuel cell is known as a redox-reaction.

Most likely a is the answer - because  you generate   38 atp's but also consume an atp.   each atp gives approx. less than 4 kcal so probably a is the closest answer.