The Displacement of a Vibrating String Versus Position Along the String

Multiple Choice

The displacement of a vibrating string versus position along the string is shown in the figure. The periodic waves have a speed of 10.0 cm/s. A and B are two points on the string.
-What is the difference in phase between the points A and B?

A) ( $\pi$ /4) radians
B) ( $\pi$ /2) radians
C) $\pi$ radians
D) (3 $\pi$ /4) radians
E) 2 $\pi$ radians