People in the Room Riddle

Puzzle of the Day 2063 :  People in the Room Puzzle

Puzzle 2063 - People in the Room Puzzle

There are 20 people in an empty, square room.  Each person has full sight of the entire room and everyone in it without turning head or body, or moving in any way (other than the eyes).

      Where can you place an apple so that all but one person can see it?