The correct option is D Optimism caused by the postwar boom
Optimism caused by the postwar boom was the most important reason for the early growth of Students for a Democratic Society (SDS) and the Free Speech Movement (FSM). Students for a Democratic Society (SDS) was American student organization that flourished in the mid-to-late 1960s and was known for its activism against the Vietnam War. Free Speech Movement, 1964 was the first revolt of the 1960s to bring to a college campus the mass civil disobedience tactics pioneered in the civil rights movement. Those tactics, most notably the sit-in, would give students unprecedented leverage to make demands on university administrators, setting the stage for mass student protests against the Vietnam War.