How do we know the sun rotates?
O
A. Both sides are blue-shifted.
O
O
O
B. One side is blue-shifted and the other side is red-shifted.
C. Both sides are red-shifted.
D. Because Earth rotates.
SUBMI

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.