 Complete the following phrase:  Charlton turned professional in 1920 and first entered the Football League in 1921. Since then the club has had four separate periods in the top flight of English football: 19361957, 19861990, 19981999, and 20002007. Historically, Charltons most successful period was the 1930s, when the clubs highest league finishes were recorded, including runners-up of the First Division in 1937. After World War II, Charlton reached two consecutive FA Cup finals, losing in 