Explain why the sound waves always reach the observer after the light waves

:The source of sound always emits the same frequency. Therefore, for the same period of time, the same number of waves must fit between the source and the observer. ... And if the source is moving away from the observer, the observer perceives sound waves reaching him or her at a less frequent rate (low pitch).

I think it's because the light waves travel faster than the sound waves.

i believe the answer would be:

d. violin, clarinet, french horn, and tuba