Kwhen an observer is moving towards a stationary object making a sound, the pitch of the sound is perceived to be fluctuating higher unchanged lower

When an observer is moving towards a stationary object making a sound,
he runs the risk of startling the stationary object.

On the other hand, if the stationary object is the one making the sound,
then the pitch of the sound perceived by the observer is higher than the
sound that the object is actually making.

Edit the post so i can see the letters for each answer, and increase the points required so i'd be able to answer it.