Under Which of These Conditions Would You Observe NO Change

Under which of these conditions would you observe NO change in perceived frequency of sound?

A) if the source is moving with a speed v and the observer moves away in the opposite direction with the same speed v
B) if the source is moving with a speed v and the observer is chasing it in the same direction with the same speed v
C) if the source is moving with a speed v and the observer moves away in the opposite direction with twice the speed v
D) if the source is moving with a speed v and the observer is chasing it in the same direction with twice the speed v