Which tenet of cell theory is described by the following paragraph about the historical observations of cells?
Early scientists were conflicted about the mechanism by which cells were created, with some scientists holding the viewpoint that cells were spontaneously crystallized in what was known as free cell formation. Robert Remak discovered ways to fix and observe cell membranes in various stages of cell division. These findings led Rudolf Virchow to proclaim in 1855, Omnis cellula e cellula (every cell comes from another cell), thus completing the tenets of cell theory.

a. E-cell is the basic unit of every organism.
b. All cells come from preexisting cells.
c. All organisms are composed of one or more cells.
d. Similar species share essentially the same chemical composition of cells.

The given paragraph tells about the process of the formation of new cells. Cells form bodies of all living beings. The older and damaged cells are replaced by the new cells. The formation of new cells is also required during growth and development. The existing cells enter into the process of cell division and form new cells. Therefore, the given information suggests that the new cells are formed when the existing cells divide.