What Are the Three Corners of an "Iron Triangle

What are the three corners of an "iron triangle"?

A) an interest group, a congressional committee, and a federal agency
B) voters, an interest group, and a federal agency
C) the states, a congressional committee, and voters
D) a foreign government, the Office of Management and Budget, and a federal agency
E) the Office of Management and Budget, an interest group, and a congressional committee