In a stringed musical instrument, the sound frequency of a particular string can be increased by
a. tightening the string.
b. increasing the string's thickness.
c. loosening the string.
d. lengthening the string.

The answer is A: tightening the string. By doing this, the string will become slightly shorter. A shorter string, when plucked or bowed, will produce a higher pitch. The other answers will have different results. Increasing the thickness, loosening the string, and lengthening the string will all cause the pitch to lower.