Sentence:  A Negro leader said today the "freedom riders" whose arrival here touched off race riots last Saturday will continue their test of Southern bus station segregation barriers. . . . [T]he Rev. Martin Luther King Jr. . . told a news conference the group met for four hours last night and decided that "the <WSD>freedom ride</WSD> must continue." 
Meaning of the word marked with <WSD> tags:  In the United States during the 1960s, any one of a number of bus trips through parts of the southern US, made by groups of civil rights activists demonstrating their opposition to racial prejudice and segregation.