Why Has the Number of Interest Groups Increased Dramatically in the Past

Why has the number of interest groups increased dramatically in the past 50 years?

A) The courts have tried to stay out of political decisions, making lobbying Congress more important.
B) The average income of most Americans has gone up faster than inflation, giving people more money to donate to interest groups.
C) Money has become less important in politics due to the public funding of elections.
D) The size of the federal government and the types of issues it has involved itself in has increased substantially.