HELP ASAP PLS I DONT UNDERSTAND #2, 3 and 5 BUT IF U CAN HELP WITH ALL PLS DO

the generally accepted parts of modern cell theory include: all known living things are made up of one or more cells. all living cells arise from pre-existing cells by division. the cell is the fundamental unit of structure and function in all living organisms.

1. efficient use of space

2. elimination of groundwater contamination

3. energy generation

4. lower carbon footprint

i think the answer is a.keratin is the pigment responsible for skin color.