Public interest groups differ from other types of interest groups in that

a$)$ unlike other interest groups, their status is like that of a charity, not a political organization.

b$)$ they claim to serve the common good, not just their own particular interests.

c$)$ they were the first political associations to use the strategy of direct mailing.

d$)$ they were the first group to abandon lobbying and take up only grassroots activism.