Why Does the Competition Between Competing Groups Lead to Policy

Why does the competition between competing groups lead to policy gridlock?

A) The interest groups have been completely absorbed by the parties that the policies are nothing more than the existing party platforms.
B) While interest groups can effectively lobby Congress, the President and the Supreme Court have a much freer hand to ignore the threats of electoral harm.
C) The presence of so many groups in the political process has made it easier for candidates to raise the kind of money needed for campaigns so that there are narrow congressional majorities.
D) Since there are many groups capable of vigorously defending themselves, it is impossible to initiate any change that imposes concentrated costs to achieve general benefits.