Please help me in this question please

Why is excretion necessary to maintain homeostasis?

Human genes only differ by less than percent. a. 1 b. 6 c. 11 d. 16

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.