Complex sentence: Bain's career on Capital Hill began in 1965, when she became Chief of Staff to Representative Sidney R. Yates (D-Ill.) who became chairman of the House Appropriations Committee's Subcommittee on Interior and Related Agencies in 1975.
Split into simpler sentences: Bain's career on Capital Hill began in 1965, when she became Chief of Staff to Representative Sidney R. Yates (D-Ill.). Yates became chairman of the House Appropriations Committee's Subcommittee on Interior and Related Agencies in 1975.