47. A light ray passes through substances 1,2 , and 3 , as shown. The indices of refraction for these three substances are n1,n2, and n3, respectively. Ray segments in 1 and 3 are parallel. From the directions of the ray, one can conclude that
(A) n3 must be the same as n1
(B) n2 must be less than n1
(C) n2 must be less than n3
(D all three indices must be the same
