Why Has the Encouragement of the Federal Government Itself Been

Why has the encouragement of the federal government itself been the most important of the dynamics behind the expanding interest group universe?

A) Congress passed laws making it easier for groups to organize such as sending mail for free.
B) Changes in the law have allowed groups to lobby more freely to ensure that members of Congress have enough information.
C) The growing scope of government activity has encouraged the proliferation of organizations in the nonprofit and public sectors.
D) The presence of gridlock has meant that the only way to break through partisan stalemate is organizing separate groups from the parties.