The best answer to the question about what caused the House Un-American Activities Committee (HUAC) to change over time is C) Senator Joe McCarthy grew its power and influence.
During the early years of the Cold War, especially in the 1950s, Senator McCarthy's aggressive anti-communist stance and methods brought significant attention to the issue of communism in America and bolstered the activities of HUAC. Although other factors mentioned can be relevant in discussing various aspects of McCarthyism and anti-communist sentiment during this time, McCarthy’s influence was a key driver in shaping the committee's activities and the public's perception of it.