Complex sentence: The Nassau County Breeders' Cup Stakes is a race for Thoroughbred horses open to three-year-old fillies willing to run the distance of seven furlongs on the Belmont Park dirt.
Split into simpler sentences: The Nassau County Breeders' Cup Stakes is a race for thoroughbred horses. It is open to three-year-old fillies willing to run the distance of seven furlongs on the Belmont Park dirt.