The Insect Body Plan Includes Many Groups of Serially Repeated

The insect body plan includes many groups of serially repeated units.For example,there are typically three pairs of legs,one on each of the three segments of the thorax.Which option best describes how these pairs of legs develop and evolve?

A) The body parts develop in a modular fashion.Therefore,a genetic change could alter the development of one pair of limbs without noticeably changing the rest of the insect's body plan.
B) A single gene controls the development of all six legs.Thus within a species,all three pairs of legs are identical.
C) The leg pairs all influence each other during development.Gene products move by diffusion from one segment to the other.Therefore,it is impossible to alter the development and form of one pair of legs without causing similar changes in the other two pairs of legs.
D) The leg pairs grow under the control of an ancient set of highly conserved genes.Therefore,all insects have more or less identical legs.Other parts of the insect body plan can evolve somewhat more freely.