How does the Doppler effect explain wavelength shifts in both light and sound?

Question $41$ options:

If an observer is receding from a source of waves, the peaks of successive waves will arrive farther apart.

If an observer has lower temperature than a source of waves, the time it takes adjacent peaks to reach the observer will be smaller.

$$If an observer is receding from a source of waves, the peaks of successive waves will arrive closer together.

If an observer has lower temperature than a source of waves, the time it takes adjacent peaks to reach the observer will be greater.