Explain Cell Differentiation Process Practice Test

In a human body, a muscle cell and a nerve cell contain the same DNA. Yet muscle cells are long and packed with proteins that help them contract, while nerve cells have long extensions that help them send signals. Which statement best explains how these two cell types can be so different even though their DNA is identical?

Early in development, an embryo begins as a single fertilized egg cell that divides many times, producing many cells with the same DNA. Later, some cells become skin cells that form a protective barrier, while others become nerve cells that transmit signals. Which idea best explains how this change happens?