The correct answer is B.
On this graph we can observe the workings of the stabilizing selection. Stabilizing selection tends to favor the average phenotype and eliminate the extremes. Essentially, this means that the natural selection is selecting the mean value of a trait as optimal. In our case, the mean weight of newborns is selected as optimal, because newborns born with less weight can be too weak to survive and the ones that have too much weight (are too big) can hurt the mother during birth.
