In the past, combining children of different ages in one classroom was usually a failure; it resulted in confused younger children, who were given inadequate attention and instruction, and bored older ones, who had to sit through previously learned lessons. Recently, however, the practice has been revived with excellent results. Mixed-age classrooms today are stimulating to older children and enable younger children to learn much more efficiently than in standard classrooms. Which one of the following, if true, most helps to resolve the apparent discrepancy in the passage? ["Today's mixed-age classrooms, unlike those of the past, emphasize group projects that are engaging to students of different ages.", 'On average, mixed-age classrooms today are somewhat larger in enrollment than were the ones of the past.', 'Few of the teachers who are reviving mixed- age classrooms today were students in mixed-age classrooms when they were young.', 'Mixed-age classrooms of the past were better equipped than are those of today.']