For a music fan, the quiz question, ‘Who wrote “This Land is Your Land”?’ might seem laughably easy. Yet if you answered ‘Woody Guthrie’, I’m afraid you only get half marks. Guthrie did write the lyrics, but following his normal practice he set them to an existing melody — in this case that of the Carter Family’s ‘When the World’s on Fire’, which they’d got from their friend Lesley Riddle, who may well have found it somewhere else.