Copying the HIV virus' nucleic acid depend on...?

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.

Why does the earth spin slowly, not faster? is it possible to prove it scientifically? can you prove it with math?

What is it called when lava when it erupts from the surface through volcanoes.