Most of the Cells of a Multicellular Eukaryote Are Genetically

Most of the cells of a multicellular eukaryote are genetically identical yet may eventually become specialized for specific tasks; how can these differences in cell function be explained?

A) Environmental gradients across the body of the organism model the cell in unique ways.
B) Each specialized cell uses sets of genes that are not expressed in other cells, thus constructing unique proteins that affect the function of the cell.
C) Cells of different organisms, each genetically distinct, must combine to produce multicellular assemblies.
D) Cells absorb differentiating substances from the environment that cause them to adapt new functions and appearances.