Complex sentence: Loudoun County High School, which serves the western portion, Heritage High School, which serves the eastern portion, and a third high school, Tuscarora High School, opened for the 2010-2011 school year.
Split into simpler sentences: Loudoun County High School, which serves the western portion, and Heritage High School, which serves the eastern portion. A third high school, Tuscarora High School, opened for the 2010-2011 school year.