Atropical climate would be and located

Which technically is nasa developing that will astronauts reach mars

Are the earth's ocean floor and continents the same age geologically? why or why not?

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.