During a cell's development, it differentiates. How does differentiation occur?
A. A developing cell's function is determined by the number of organelles it contains.
B. A developing cell receives hormonal messages from endocrine glands that instruct the cell's chromosomes.
C. As a cell matures, genes that are not necessary to its function are ejected out of the cell through active transport.
D. Certain genes are turned on and others are turned off; this action produces adult cells that are specialized.