Complex sentence: Service from Concord to MacArthur began on May 21,1973, and the line was extended to Daly City when the Transbay Tube opened on September 16,1974.
Split into simpler sentences: Service from Concord to MacArthur began on May 21,1973. The line was extended to Daly City when the Transbay Tube opened on September 16,1974.