In an insect,

a. nutrients are circulated through an open circulatory system.
b. the blood vessels do not form a continuous circuit
c. the fluid flowing through the heart is the same fluid that bathes the tissues.
d. the circulatory system is responsible for exchange of respiratory gases

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.