Which organ systems are used to help the body shiver

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.

Black fur(b) in guinea pigs is dominant over white fur(b). find the probability of a homozygous offspring in a cross: bb x bb. a. 0% b. 25% c. 50% d. 75% e. 100%

During photosynthesis, hydrogen ions are most directly used to in the chloroplast pictured above. a) make glucose b) make chlorophyll c) produce carbon dioxide d) drive the production of atp