请阅读 Passage1,回答21-25问题。
Passage 1
In a traditional classroom, much, if not most, of class time is spent with the teacher presenting content -telling, showing, explaining and lecturing．Whether it’s a first-grade teacher reading to students, a high school government teacher lecturing on the Articles of Confederation, or a math teacher demonstrating how to solve an equation, class time is when the teacher delivers information and the students receive it
Ideally, lessons involve a mixture of delivery and discussion, supplemented by activities that engage students to support their comprehension．But in reality, just getting the content across can take most of the class period, especially when lessons are interrupted by student questions, discipline problems, and distractions like fire drills, assemblies, and other disruptions.
There are lots of good reasons for this model and its durability in education．It is an efficient way to assure that all students have access to the same course content, and it provides a way for teachers to transmit their expertise in a subject, and enthusiasm for it, to their students．Most teachers love being the “sage on the stage”, and many are very good at it.
Nevertheless, many teachers also feel frustrated by the limitations of this model, especially when lecture and presentation take up the lion’s share of the class period, leaving little time for the good stuff of teaching—getting into students’, helping them make meaning out of information, drawing out their evolving understanding, encouraging and sparkling their excitement and comprehension．In today’s environment of high-stakes testing, with multiple standards—and now with the Common Core, new standards—there never seems to be enough time for all the things teachers wish they could do with their students: project-based activities, individual or group learning challenges, deep discussions and inquiry activities.
So it’s not surprising that, when teachers are asked what they believe is the greatest value of flipping instruction, the answer is almost always, “It gives me more time to work directly with students during class.” Teachers at Michigan’s Clintondale High School claim that, since they have flipped their classrooms, the amount of time they spend with students has increased by a factor of four．That is substantial gain— and it makes a real difference in students believing that the teacher is there for them when help is needed.