What motivates Pacific salmon to migrate? And give two obstacles they face during migration.

Plz ! ive been stuck on this forever

Give an example of a trait that is controlled by more than one gene.

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.