The answer is when the cell express different genes.
Explanation:
Cell differentiation is the process when a cell is changed from one cell type to an other and brings more complexity to the system. A cell before differentiation possess all the genes however their expression in turned off. When some external or internal factors trigger the gene expression it starts the cell differentiation. A multicellular organism undergoes several rounds of cell differentiation during its development. Although cell differentiation changes the size, shape and metabolic activity but the genetic makeup or DNA is never changed during cell differentiation.
This statement giving a clue that there is asexually reproduction (may be binary fission) taking place and the progenies in asexual reproduction are genetically similar to parent cell. So answer is A.
