Which final discovery about cells led to the development of the cell theory?

a. all organisms are composed of one or more cells.
b. the cell is the basic unit of organization in organisms.
c. all cells have a nucleus.
d. all cells come from preexisting cells.

The answer is A

By the late 1830s, botanist Matthias Schleiden and zoologist Theodor Schwann were studying tissues and proposed the unified cell theory. The unified cell theory states that: all living things are composed of one or more cells; the cell is the basic unit of life; and new cells arise from existing cells.

a. the production of carbon dioxide through the process of photosynthesis

the wires in the toaster turning red and the toast crisping and turning brown