The Figure Shows Two Sets of Waves, Created by Two

The figure shows two sets of waves, created by two sources labeled "A" and "B." The solid
Half- circles represent wave crests from A, and the dashed half- circles represent wave crests from B. Suppose that individual wave crests from either source A or source B alone are 3 mm above the level of the undisturbed water. Then the displacement of the water [above or below the level of the undisturbed water] at the point marked "x" [with the arrow pointing toward it] is

A) - 3 mm.
B) +6 mm.
C) 0 mm.
D) - 6 mm.
E) +3 mm.