Complex sentence: In 1979, the BGA opened new offices in Washington, D.C., and Springfield, Illinois; the D.C. office, however, was too expensive and was closed n 1984.
Split into simpler sentences: In 1979, the BGA opened new offices in Washington, D.C. and Springfield, Illinois. The D.C.-based office, however, was too expensive to maintain and was closed n 1984.