The answer is A. Voltaic cells couple oxidation and reduction half reactions to produce electromotive force from chemical potential energy. Electrolytic cells do the opposite in that they require electromotive force to store chemical energy.
<u><em>Ponds and rivers are two types of . . . . freshwater ecosystems</em></u>
I believe the SI unit for length is meters and I'm sure that the SI unit for mass is kilogram
