SALEM, VAF;or the eighth straight world-history period, sophomores at Riverside High School watched the 1959 classic Ben-Hur Tuesday. 'The chariot races were pretty cool,' Michael Bower said of the 211-minute film he and classmates have been watching in 25-minute segments, between roll call and free-reading. 'And when Mr. Franks got back from the teachers' lounge, he told us Jesus is in tomorrow's part.' Bower said he dreads next week, when the class will break into Ben-Hur discussion groups and share their ancient-history unit journals. 