Which of the following best describes how friction affects motion? A
Friction makes motion between two touching surfaces much easier.
Sliding friction makes running on a windy day much harder on your body.
-АВ
Rolling friction makes moving through liquids feel like very hard work.
D
Friction makes motion between two touching surfaces more difficult.

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.