How is the wavelength of sound affected when a sound source moves toward a stationary observer, and the observer moves away from a stationary sound source?

Question

(a)
when a sound source moves toward a stationary observer
The wavelength is shortened.
The wavelength is lengthened.
(b)
when the observer moves away from a stationary sound source
The wavelength is shortened.
The wavelength is lengthened.

Answer 1

(a) The wavelength is shortened when a sound source moves toward a stationary observer.
(b) The wavelength is lengthened when the observer moves away from a stationary sound source.