Before a new medicine is approved, scientists study the effects the medicine has on different parts of the body. Often, a medicine is tested on mice before it is tested on humans. All the cells in the illustration below came from the same mouse.

Four images of unique looking cells

If all of these cells are mouse cells, why do they look so different from each other?

A. Cells change shape as they get older.
B. Different cells specialize in different functions.
C. Each kind of cell is from a different organ system.
D. Different-shaped cells came from different ancestors.