Question 15
A robot bee has four arrow buttons on its back. It moves on a square-tiled floor. The buttons mean:
Move forward one tile.
Turn left 90° without moving.
Turn right 90° without moving.
Move backward one tile.
Another button marked GO executes the stored program. For example, the following sequence moves the bee to the position shown.
The bee remembers its program, so pressing GO again executes it again from its new position and direction. You may repeat as often as desired. Repeated GO presses eventually return the bee to its starting place for all but one program below. Which is the exception?
Move forward one tile.
Turn left 90° without moving.
Turn right 90° without moving.
Move backward one tile.
Another button marked GO executes the stored program. For example, the following sequence moves the bee to the position shown.
The bee remembers its program, so pressing GO again executes it again from its new position and direction. You may repeat as often as desired. Repeated GO presses eventually return the bee to its starting place for all but one program below. Which is the exception?
