Two Sources of Waves, Call Them a and B, Send

Multiple Choice

Two sources of waves, call them A and B, send out waves across the surface of a lake. The waves from A have crests 1 cm high as measured from the normal undisturbed surface of the water. The waves from B are identical to those from A. How far is the water displaced at a point where a valley from A crosses a valley from B?

A) 1 cm upward
B) zero
C) 1 cm downward
D) 2 cm downward
E) 2 cm upward