Answer:
a.) Biomass is the total mass of biological material, both living and recently dead, in a defined area.
b.) The Sun's light is the original source of these energy forms. Both are formed into original material by photosynthesis, sunlight combining carbon dioxide and water into plant matter.
c.) Coal, oil and natural gas (or methane).
d.) Non-renewable resources cannot be naturally replaced in a small enough timescale for us to have an unlimited supply. When we have run out, it will take natural processes millions of years to form them again.