The correct answer is: "a student organization that opposed the war in Vietnam".
The Students for a Democractic Society (SDS) is a left-wing student activist organization that emerged in 1960. It quickly developed along the decade, with more than 300 branches all over the country, before its disolution in 1969. It leaded protests against Vietnam War, which was a viewpoint that was increasingly gathering support amongst the US public opinion. Subsequently, SDS has influenced other student movements in the next decades.
