Complex sentence: "The Unnatural" originally aired in the United States on the Fox network on April 25,1999, and was first broadcast in the United Kingdom on Sky1 on July 4,1999.
Split into simpler sentences: The Unnatural first aired in the United States on April 25,1999, on the Fox network. In the United Kingdom, the episode was first broadcast on Sky1 on July 4,1999.