7. which of the following would lower the pitch of a string instrument's sound?

a. adding tension within the string.
b. shortening the effective string length.
c. increasing the thickness of the string used.
d. using less force to vibrate the string.

The correct option is C.

The pitch of a string refers to the quality of sound that is produced by the string when it vibrates. There are three basic factors that affect the quality of pitch of a string, these are: the tension, the thickness of the string and the length of the string. The higher the thickness of the string, the lower the pitch of the string, thus, increasing the thickness of the string will lower the pitch.

the answer is true.