In the history of cell biology, which set correctly lists the three classical tenets of cell theory?

• A. All cells have cell walls; the cell is the basic unit of heredity; all organisms are composed only of tissues.
• B. All cells contain a nucleus; all organisms reproduce sexually; all cells arise spontaneously from nonliving matter.
• C. Cells are the smallest observable structures; cells are identical in all organisms; all cells are formed by fusion of smaller particles.
• D. All living organisms are composed of one or more cells; the cell is the basic unit of structure and function in organisms; all cells arise from pre-existing cells.

Answer: (D)