In the Laboratory,fruit Flies (Drosophila)were Artificially Selected for the Number

In the laboratory,fruit flies (Drosophila) were artificially selected for the number of bristles on their bodies.One population (R) was selected for low numbers of bristles,a second population (S) for high numbers of bristles.

-In order for the scientists to artificially select Drosophila for their number of bristles,

A) they had to induce mutations into their populations of Drosophila.
B) they had to study the population for millions of years.
C) genetic variation had to be present in the population.
D) dramatic mutations had to be produced by the selection.
E) the number of bristles in each Drosophila had to be random.