A

Step 1: Understand the Doppler Effect, which describes the change in frequency (or wavelength) of a wave in relation to an observer moving relative to the wave source.
Step 2: When the listener and the sound source move at right angles to each other, the relative velocity between them is important. The frequency observed by the listener is dependent on the component of the velocity of the source and listener along the line connecting them.
Step 3: As the listener moves in a direction perpendicular to the direction of the sound waves, the frequency changes due to the fact that while the sound waves are coming at a constant speed, the listener is not closing the distance to the sound source effectively. Therefore, while there is a change in frequency, it is not as pronounced as in the case of direct approach or receding.
Step 4: The formula used here is given by:
\( f' = f \frac{v + v_l}{v + v_s} \)
where \( f' \) is the observed frequency, \( f \) is the source frequency, \( v \) is the speed of sound in the medium, \( v_l \) is the velocity of the listener (positive if moving towards the source), and \( v_s \) is the velocity of the source (positive if moving away).
Since the movement is perpendicular, \( v_l \) does not effectively contribute to an increase or decrease in frequency due to the geometry of the situation.
Therefore, due to the change in relative motion, the listener hears a different frequency than what is emitted. Thus, the statement is true.
Therefore, A.