Complex sentence: Elvington was part of the East Riding of Yorkshire until local government boundary changes in 1974 when it became part of the Selby district in North Yorkshire and subsequently in 1996 became part of the City of York unitary authority.
Split into simpler sentences: Elvington was part of the East Riding of Yorkshire until local government boundary changes in 1974, when it became part of the Selby district in North Yorkshire. In 1996 it became part of the City of York unitary authority.