Complex sentence: Our Lady of Solace school building remained vacant until September 2010, when the Bronx Charter School of Excellence annex opened; the school's main site is at Benedict Avenue, while the Holland Avenue site serves as only an annex for grades five and six.
Split into simpler sentences: Our Lady of Solace school building remained vacant until September 2010 when the Bronx Charter School of Excellence opened. The Bronx Charter School of Excellence has its main location at Benedict Avenue while the Holland Avenue site serves as only an annex for grades five and six.