A diver in swimming pool wants to signal his distress to a person lying on the edge of the pool by flashing his water proof flash light.

Options

A. He must direct the beam vertically upward
B. He has to direct the beam horizontally
C. He has to direct the beam at an angle to the ertical which si slightly less than the critical angle of incidence for total reflection.
D. he has to direct the beam at an angle to the vertical which is slightly more than the critcal angle of incidence for total reflection.