Which set of statements best summarizes the main points of classical cell theory?

• A. 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.
• B. Energy is produced only in mitochondria; cells can arise spontaneously from nonliving matter; all cells are the same size and shape.
• C. All cells contain a nucleus; all organisms reproduce only sexually; all traits are inherited solely through proteins.
• D. All organisms are made of tissues; tissues are the basic unit of life; all tissues arise from pre-existing tissues.

Answer: (A)