The answer is:
a) The properties of sound determine the pitch of sound is the frequency
The explanation:
The pitch of sound is affected by frequency of the sound as higher frequency will give higher pitch of the sound .
b) This will affected by motion of the sound source:
when the frequency is : the number of waves per second , So when the sound source moves faster the frequency will be increased as when the source moves faster the number of waves will be increase per time so the frequency will be higher
and as the frequency get higher so, that effect the pitch of sound and makes it higher.