Why Is Grassroots Lobbying an Effective Political Tactic

Why is grassroots lobbying an effective political tactic?

A) Grassroots lobbying shapes public opinion,and elected officials are known to respond to public opinion.
B) Interest groups rarely engage in grassroots lobbying,so when they use this tactic,elected officials take notice.
C) Grassroots lobbyists collect and bundle together campaign contributions from multiple individuals.This results in one large campaign contribution and thus maximizes the impact of each contributor.
D) Grassroots lobbying depends on building personal connections with elected officials,who are more likely to listen to groups that they know and like.