Answer:
The answer is A. Cell.
Step-by-step explanation:
The cell is the anatomical, basic, structural, functional and fundamental unit of all living organisms, which is microscopic and is formed by cytoplasm, one or more nuclei and a surrounding membrane. The cell is the smallest element size that can be considered alive. Living organisms can be classified according to the number of cells they possess, that is, if they only have one, they are called unicellular; while if they have more, they are called multicellular. the cells form organs, which in turn form the species, which make up an ecosystem.