premise: Sparta is an American rock band from El Paso, Texas, formed in 2001. Founding members Jim Ward (vocalist/guitarist) and Tony Hajjar (drummer) are also members of post-hardcore group At the Drive-In. Keeley Davis (guitarist) is the former frontman of Engine Down.
hypothesis: Sparta was not formed in the 20th century.
reason: It's definitely correct because they were formed in 2001, which is the 21st century. It's difficult because the sentence is framed in the negative, which the system seems to have trouble dealing with.