The correct answer is C. Students for a Democratic Society
Step-by-step explanation:
The Vietnam war was a conflict from 1955 to 1973 in which the United States participated to support North Vietnam against South Vietnam that was supported by China and the Soviet Union. The involvement of the U.S. in the war was mainly controversial and opposed by American citizens based on moral arguments as many considered the role of the United States was immoral or not justifiable. This included multiple groups such as mothers, hippies, students that led peace movements.
In the case of students, one of the major organizations was the Students for a Democratic Society that was created in 1960 and although it first supported the civil rights movement also involved in the opposition to the Vietnam War leading multiple marches, protest and demonstrations all around the country as it included delegates from different states. Therefore, the one that was one major student organization that was against the Vietnam war was the Students for a Democratic Society.