Complex sentence: Southern Okanagan Secondary was a public high school in Oliver, British Columbia (part of School District 53 Okanagan Similkameen) until September 12,2011 when the majority of the school was engulfed in flames.
Split into simpler sentences: Southern Okanagan Secondary is a public high school in Oliver, British Columbia (part of School District 53 Okanagan Similkameen). On September 12,2011 the majority of the school was engulfed in flames.