What causes the soils in former rain forests to deplete so quickly after they are used for farming? frequent rain hot temperatures reforestation slash-and-burn techniques

Which revelation resulted from the observation of the spectrum of different galaxies? a. there were more galaxies whose spectrum was blueshifted b. there were no galaxies whose spectrum was redshifted c. there were more galaxies whose spectrum was redshifted d. there were no galaxies whose spectrum was blueshifted