The arousal of anger is sometimes a legitimate artistic aim, and every legitimate artwork that has this aim calls intentionally for concrete intervention in the world. Even granting that most art is concerned with beauty in some way, it follows that those critics who maintain that a concern for beauty is a characteristic of all legitimate art are mistaken. The conclusion of the argument follows logically if which one of the following is assumed? ['No works of art that call for intervention are concerned with beauty.', 'Only works that call for intervention are legitimate works of art.', 'Only those works that are exclusively concerned with beauty are legitimate works of art.', 'There are works that are concerned with beauty but that are not legitimate works of art.']