Answer:
im not very smart but i think b or c
Explanation:
The density, of a substance is its mass per unit volume. basically is mass so its one of the two. i hope i helped! <3
D because if you are trying to reduce the carbon footprint then using less coal or oil based energy would be best. plus using the solar panels will help because all you have to rely on is the sun and your own power bank for energy. there for leaving less of a carbon footprint.
