They became nerve cells. They became red blood cells. They became bone cells. They became skin cells.
Stem cells are cells that can differentiate into many different kinds of cells. Scientists have discovered that the environment supporting the cells influences stem-cell differentiation. For example, stem cells grown on strong, flexible surfaces became muscle cells. What most likely happened to stem cells grown on a hard, rigid surface?

Options:
- They became nerve cells.
- They became red blood cells.
- They became bone cells.
- They became skin cells.

They became bone cells.