20. A student performed Young's double-slit experiment in air using red light. When he immersed the apparatus in water repeated the experiment, what happens to the interference pattern on the screen? (A) No change happens in the interference pattern. (B) The bright and dark fringes stay in the same locations, but the contrast is reduced. (C) It disappears. (D) The bright fringes are farther apart. (E) The bright fringes are closer together.