Answer:
a. Developing cells may express different parts of their identical genetic instructions.
Step-by-step explanation:
Humans are multicellular organisms i.e. we possess many cells in our body. These cells increase as a result of division. Although all of the cells of humans develop from one fertilized egg (zygote), the human is born with many different types of cells because of a process called CELL DIFFERENTIATION.
Cell differentiation is a process in multicellular organisms where a cell becomes more specialized in function as it divides. The set of genes contained in each cell are not expressed simultaneously i.e. some genes are expressed while others are repressed. This is how cells with the same gene possess different functions. Therefore, according to this question, developing cells may express different parts of their identical genetic instructions to be of different types.