Complex sentence: Their first single release in 1959 was a cover version of Paul Evans and the Curls' Stateside hit song "Seven Little Girls (Sitting in the Back Seat)", written by Bob Hilliard and Lee Pockriss.
Split into simpler sentences: Their first single release in 1959 was a cover version of Paul Evans and the Curls', Stateside hit song, "Seven Little Girls (Sitting in the Back Seat)". The song, "Seven Little Girls (Sitting in the Back Seat)", was written by Bob Hilliard and Lee Pockriss.