In the history of cell biology, what was Rudolf Virchow's key contribution to cell theory?

• A. He concluded that the nucleus is essential for cell division and heredity, based on studies of fertilization.
• B. He developed the idea that all living organisms are composed of one or more cells as the basic unit of life.
• C. He proposed that all cells arise from pre-existing cells ("Omnis cellula e cellula").
• D. He first observed living cells and coined the term "cell" after viewing cork under a microscope.

Answer: (C)