Complex sentence: In 1955, Marianapolis officially became a part of the New England Association of Secondary Schools and Colleges and in 1974 finally became co-educational due to low enrollment after the Oil Crisis of the 1970s.
Split into simpler sentences: In 1955, Marianapolis officially became a part of the New England Association of Secondary Schools and Colleges. In 1974 finally became co-educational due to low enrollment after the Oil Crisis of the 1970s.