Complex sentence: In the fall of 1953, St. Joseph Parochial Elementary School, built by St. Joseph Parish, opened and Bethlehem then became a parish high school for girls, no longer owned by the Sisters, but staffed by them.
Split into simpler sentences: In the fall of 1953, St. Joseph Parochial Elementary School, built by St. Joseph Parish, opened. Bethlehem was operated exclusively as a parish high school for girls, no longer owned by the Sisters, but staffed by them.