Answer:
A) cell theory
Step-by-step explanation:
Cell theory is widely accepted theory that exclaims that all living things are composed of basic units-cells. Living organisms might be composed of one cell-unicellular organisms or more than one-multicellular organisms.
There is only one exception-viruses. Viruses are non-cellular entities but they are considered as living forms.
Robert Hooke is responsible for the creation of this theory.