The hydra has an incomplete digestive system.

how does the hydra remove undigested food?

a.
it pulls food out with its tentacles.

b.
it pushes out food through an opening, which is also used to bring in food.

c.
it diffuses food through its outer layer.

d.
it expels food by using a special opening for that purpose.

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.