Music historian: In the past, radio stations would not play rock songs that were more than three minutes in length. Rock musicians claimed that such commercial barriers limited their creativity, and some critics argue that only since those barriers have been lifted has rock music become artistic. In fact, however, when these barriers were lifted, the standards for song structures broke down and the music became aimless, because the styles from which rock derived were not well suited to songs of extended length. Which one of the following is most strongly supported by the music historian's claims? ['Rock music can sometimes benefit from the existence of commercial barriers rather than being harmed by them.', 'Rock music is not a good outlet for creative musicians who have a great many ideas.', 'Rock music requires more discipline than some other forms of music.', 'Rock music must borrow from styles more conducive to songs of extended length if it is to become artistic.']