Three observers, A, B, and C are listening to a moving source of sound. The diagram below shows the location of the wavecrests of the moving source with respect to the three observers. Which of the following is true?

GREEN: The wavefronts move faster at A than at B and C.

YELLOW: The wavefronts move faster at C than at A and B.

BLUE: The frequency of the sound is highest at A.

PINK: The frequency of the sound is highest at B.

PURPLE: The frequency of the sound is highest at C.