What Is the Difference Between Grassroots/outside Lobbying and Lobbying Members

What is the difference between grassroots/outside lobbying and lobbying members of Congress directly?

A) Only multi-issue interest groups attempt to lobby members of Congress directly.
B) Grassroots/outside lobbying is a technique that places pressure on elected officials using group members and/or general public opinion.
C) Grassroots lobbying faces key barriers, but direct lobbying does not.
D) These two types of lobbying are essentially the same thing.