Complex sentence: Athletic teams compete in either the Rhode Island Interscholastic League or the SENE division of the New England Preparatory School Athletic Conference, and each year at least 30% of the teams compete in league championships.
Split into simpler sentences: Athletic teams compete in either the Rhode Island Interscholastic League or the SENE division of the New England Preparatory School Athletic Conference. Teams compete in either the SENEISSA or RIIL leagues, and each year at least 30% of the teams compete in league championships.