Please choose the correct answer to the 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?

Answer1: They became nerve cells. Answer2: They became red blood cells. Answer3: They became bone cells. Answer4: They became skin cells.

Answer format: answer1/answer2/answer3/answer4