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

• A

  He must direct the beam vertically upwards

• B

  He has to direct the beam horizontally

• C

  He has to direct the beam at an angle to the vertical which is slightly less than the critical angle of incidence for total internal reflection

• D

  He has to direct the beam at an angle to the vertical which is slightly more than the critical angle of incidence for the total internal reflection