Complex sentence: RCA executive Dennis Katz had complained that the album did not contain a single, so Bowie wrote "Starman", the last song to be written, which was completed on 4 February 1972.
Split into simpler sentences: RCA executive Dennis Katz had complained that the album did not contain a single. Then, Bowie wrote "Starman", the last song to be written, which was completed on 4 February 1972.