Question

which part of the cell theory is best explained by studying the ability of stem cells to divide and form additional cells?
all cells come from preexisting cells.
cells are the basic units of structure and function of all living things.
all organisms are composed of cells.
all cells are similar in composition and metabolic activities.

Explanation:

Stem cells dividing to form new cells shows new cells originate from preexisting stem cells. This matches "All cells come from preexisting cells". Other options relate to cell as unit, organism composition, or cell similarity, not cell origin via division.

Answer:

A. All cells come from preexisting cells.