Biology

The cell is the basic structural and functional unit of all living organisms. Every living organism is made up of cells, which carry out the essential processes required for life. Cells can exist as single-celled organisms (e.g., bacteria) or as part of multicellular organisms (e.g., humans, animals, plants).

For A: Atoms are the building blocks of matter, but they are not living units. They combine to form molecules, but on their own, they do not carry out life processes.
For B: An organ is a gr...