C
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
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?

### Choices:
A. They became nerve cells.
B. They became red blood cells.
C. They became bone cells.
D. They became skin cells.

### Answer:
