Complex sentence: In 1991, a major extension to the school site added 19 classrooms, four laboratories, two computer rooms, a sports hall, library, and the former school gymnasium extended to become the Russell Hall, the senior school assembly hall and theatrical stage.
Split into simpler sentences: In 1991, a major extension to the school site added 19 classrooms, four laboratories, two computer rooms, a sports hall and library. The former school gymnasium was extended to become the Russell Hall, the senior school assembly hall and theatrical stage.