A seismograph records four earthquakes of magnitude 3.7, 3.2, 6.5 and 4.3 and then seismicity decreases. Which earthquake(s) represent (a) foreshock(s)

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