Why Has the Number of Interest Groups Gone Up Dramatically

Why has the number of interest groups gone up dramatically in the pasty 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.
E) Congress has increased in size thus allowing for more lobbying opportunities.