The Experiment in Which Drosophila Flies Were Raised at a Higher-Than-Normal

The experiment in which Drosophila flies were raised at a higher-than-normal oxygen concentration led to which of the following conclusions?

A) Fly body size is constrained because there are not enough alleles that increase body size.
B) Fly body size is constrained because alleles that increase body size are selected against at normal oxygen levels.
C) At normal oxygen concentration levels, fly body size is under strong directional selection.
D) Fly body size would likely increase if flies were raised at lower-than-normal oxygen concentrations.
E) Increased oxygen levels appear to have little effect on fly body size, even after many generations.