Which force requires contact? A. The force of attraction between two masses

B. The force produced by interactions between electrically charged objects

C. The force exerted by air as an object moves through it

D. The force producers by interactions between magnetic objects

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.