Answer:
b) I shall be speaking on the joys of volunteerism
Step-by-step explanation:
The best way to atract volunteerism would be to explain to potential volunteers that the mere action of helping other will give them joy. I think this is the best because it promises joy for volunteers, which is something so simple and, at the same time, so attractive.
The rest of the options a, c and d are about receiving something in return for volunteering.