While Camping, Alicia and Seth Saw a Bright Light in the Distance

Multiple Choice

While camping, Alicia and Seth saw a bright light in the distance on a very dark night. After watching it for a few moments, it suddenly began to move. If they looked away and then looked back, it appeared to hover in one spot, then start moving again. They told their friends they had seen a UFO. Really, they had been fooled by _____

A) stroboscopic motion.
B) the motion parallax.
C) the autokinetic illusion.
D) the principle of continuity.