A String of Lights in a Store Window Are Set

Multiple Choice

A string of lights in a store window are set up in such a way that one light flashes, followed by a second one that is adjacent to the first, followed by a third one, etc.
-If the timing between flashes is 60 milliseconds, what will observers perceive?

A) the phi phenomenon
B) no movement
C) an object moving through space
D) no lights