Why do small interest groups have an easier time enrolling potential members than do large interest groups?

A. In a small group, any individual’s share of the collective good may be great enough to make it rational for him or her to join.
b. In a small group, only individuals who contribute to the group’s efforts can enjoy the collective good.
c. Small groups are able to offer material incentives, whereas large groups are not.
d. Unlike large groups, small groups often receive the help of patrons in recruiting members.

Aparagraph would strengthen it the most