In the Furrow Illusion, When the Image Is Set in Motion

In the furrow illusion, when the image is set in motion, the yellow circles move from left to right or right to left across the large gray and white circle.But when a person focuses on the top yellow circle ______.

A) the gray and white circle appears to expand in size
B) the gray and white circle appears to shrink in size
C) the top yellow circle appears to spiral as it makes its way across the screen
D) the lower yellow circle appears to zigzag back and forth as it heads across the screen