Which statement is true for both incomplete and complete digestive systems?
a. materials enter and exit through the same opening.
b. digestion begins outside the cells.
c. the digestive cavity is like a tube.
d. continuous feeding is possible.
pretty sure it's b

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.