Which two organs can both chemical and mechanical digestion take place? A: Esophagus, Mouth
B: Mouth, Stomach
C: Small Intestine, Liver
D: Large Intestine, Stomach

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.