Many golfers wear wrist bracelets containing magnets because they claim the magnets improve balance and the length of shots played off the tee. A golfer would like to determine if the claim has merit and finds 200 volunteers who play golf to participate in an experiment. Half of the golfers are randomly assigned to wear a bracelet with magnets, while the other half wear a bracelet without magnets. Each golfer plays normally for a month, after which the length of their shots in a subsequent round is recorded. What is the response variable in this experiment?

a. the age of each golfer
b. the 200 volunteers
c. the length of shots played by the golfers
d. whether the golfers wear or do not wear the bracelet