In the 1920s, Edwin Hubble looked at the spectra of stars from distant galaxies. To his surprise, he found that all of these spectra were red-shifted, and that the more distant the galaxy, the greater the red-shift. What is a reasonable conclusion from this evidence?

A. The universe is expanding.
B. The universe is contracting.
C. The universe is unchanging.
D. The universe is curved.

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.