Why is the cell theory considered a scientific theory? A. It has always been proven to be correct. B. It was proposed by several scientists. C. It was formed over 100 years ago. D. It is an explanation that is well supported.

Cell theory. In biology, cell theory is a scientific theory that describes the properties of cells, the basic unit of structure in every living thing. The initial development of the theory, during the mid-17th century, was made possible by advances in microscopy; the study of cells is called cell biology.