3. A source with frequency fs emits spherical sound waves. The source moves at a constant speed to the right and at a given moment three observers located at A, B and C are listening to the source. The diagram shows the location of the wave crests of the moving source with respect to the observers. a. Compare the observed frequencies at A, B, and C (rank smallest A to largest). Justify your reasoning. B b. Compare the wavelengths of the sound wave at A, B and C (rank smallest to largest). Justify your reasoning. C