Which of the following is the best example of a solidarity incentive?
a. participating in a special interest group that has weekly meetings to discuss your passion for a specific topic
b. participating in a special interest group that gives you a 10 percent monthly discount on gasoline for an annual membership
c. joining an advocacy group who stages sit-ins at your city hall each week
d. joining an interest group that gathers signatures to add a stop sign to a street in your neighborhood