The Shape of the Beak of a Hummingbird (Very Long

The shape of the beak of a hummingbird (very long and thin) and that of a finch (short and fat) is controlled by the same set of genes. Which of the following could account for the differences between these two bird beaks?

A) Apoptosis occurs in the beak of the finch, but not in the beak of the hummingbird.
B) Although development is controlled by the same genes, the genes produce different proteins and those proteins cause development to occur in different ways.
C) The hummingbird retains stem cells for a longer period of time during development than does the finch.
D) The genes involved in determining beak shape stay on for different lengths of time in each bird.