The correct option is A Virchow
Two German biologists M. J. Schleiden (1838) and Theodore Schwann (1839), proposed the cell theory. According to the theory, all living organisms are composed of cells, which are the smallest entities that can be called as 'living'. Cells are the functional unit of an organism. Schleiden stated that “all the tissues are made up of individual cells". A German biologist Rudolph Virchow observed that all living cells arise from pre-existing cells ('omnis cellula e cellula') which was added to the cell theory as a doctrine.
So, the correct answer is option A.