Answer:
D. Gene expression is regulated so that different genes are turned off and on at specific times during development of a multicellular organism.
Explanation:
In biology, cell differentiation is the process by which living cells "specialize" to perform a given function.
This process results from the differential expression of genes and is an ontogenetic process that occurs in the development of multicellular beings. Cells proliferate, differentiate, migrate and interact with each other and with the extracellular matrix, forming different tissues and organs.
In other words, the process of specialization in the cells of multicellular organisms occurs when gene expression is regulated so that different genes are turned off and linked at specific times during the development of a multicellular organism.
