If you want to change the pitch of a sound, you have to change the

If you want to change the pitch of a sound, you have to change the frequency.

Explanation:

Pitch of the sound is directly related to the frequency at which it is produced. Hence increasing the frequency of the sound will consequently increase the pitch of the sound and reducing the frequency will decrease the pitch of the sound. To get the required pitch, one should have good control over the frequency at which the sound is produced.

half of a circle

explanation:

the arrow and the top of the circle is matching together. it is not a polygon because a polygon would always be the same shape. therefore, an half of a circle is called semicircle so you would find the radius of it.

real, smaller and upside-down.   so the answer should be b.