The frequency of genes that lead to favorable traits increases because A.
favorable traits always start out as the rare form and become more common
B.
the genes for favorable traits are dominant over those for unfavorable genes
C.
Both B and D
D.
those genes continue on to the next generation when the individuals that contain the genes successfully survive and reproduce

D.

those genes continue on to the next generation when the individuals that contain the genes successfully survive and reproduce

Explanation:

This is the process of natural selection: organisms with more favorable traits will be able to survive better and pass those traits onto their offspring. They do not necessarily always start out in the rare form as stated in A and they don't always have to be dominant to appear in the gene pool as stated in B. Therefore, the answer is D. those genes continue on to the next generation when the individuals that contain the genes successfully survive and reproduce

answer///africa and asia;