The Sequence and Actions of Genes Controlling Development of the Anterior-Posterior

The sequence and actions of genes controlling development of the anterior-posterior axis of Drosophila illustrate:

A) hierarchical control of gene regulation during development.
B) the effect of maternal development on the development of the embryo.
C) that genes controlling development are turned on in groups, with each group refining the pattern of differentiation generated by previous groups.
D) that genes controlling development are turned on in sequence, with each set acting on a different set of cells to specify the cells' ultimate fates.