Which of the following scenarios is an example of using potentially copyrighted material?

a. burt started saying "you're a gold star! " each time someone scored a point on the basketball team after he heard dennis start using the phrase.
b. sacha wears a pair of legwarmers, and her older sister fawn argues that she made legwarmers a local trend.
c. fred uses a voice recording of sally for his next music video.
d. tina decided to use a dance routine that her instructor created and showed her for one of her theatrical productions.