Will give brainliest! Which statement is TRUE?

1)Light waves always travel at a constant speed, but sound waves do not.

2)Waves travel at different speeds through different materials.

3)Wave speed depends on the amplitude of the wave.

4)Light waves and sound waves travel at the same constant speed.

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.