question: <image 1>A beam of light passes from medium 1 to medium 2 to medium 3 as shown in the diagram. What may be concluded about the speed of light in each medium?
  Options: A: v_3 > v_1 > v_2, B: v_1 > v_2 > v_3, C: v_1 > v_3 < v_2, D: v_2 > v_3 > v_1