Which option correctly lists the three classical tenets of cell theory as formulated in the 19th century?

• A. All organisms are composed of tissues; tissues are the basic unit of life; tissues arise from pre-existing tissues.
• B. Cells are smaller than atoms; cells spontaneously arise from nonliving matter; cells do not require energy to function.
• C. All cells contain a nucleus; all cells have a cell wall; all cells photosynthesize to produce energy.
• D. All living organisms are composed of one or more cells; the cell is the basic unit of structure and function in living things; all cells arise from pre-existing cells.

Answer: (D)