Exhibit 18-1
the Figure Below Shows Wave Crests After a Stone

Multiple Choice

Exhibit 18-1
The figure below shows wave crests after a stone is thrown into a pond.

Use this exhibit to answer the following question.
-Refer to Exhibit 18-1.The phase difference in radians between points A and D is

A) $\pi$ .
B) 2 $\pi$ .
C) 3 $\pi$ .
D) 4 $\pi$ .
E) 5 $\pi$ .