Two Point Sources Emit Sound Waves of 1

Multiple Choice

Two point sources emit sound waves of 1.0-m wavelength.The sources,2.0 m apart,as shown below,emit waves which are in phase with each other at the instant of emission.Where,along the line between the sources,are the waves out of phase with each other by π radians?

A) x = 0,1.0 m,2.0 m
B) x = 0.50 m,1.5 m
C) x = 0.50 m,1.0 m,1.5 m
D) x = 0.75 m,1.25 m
E) x = 0.25 m,0.75 m,1.25 m,1.75 m