"Do you know what the most complex mass of protoplasm (原生质) on earth is"Marian Diamond asks her students on the first day of anatomy class as she casually opens a flowery hatbox and lifts out a preserved human brain. "This mass only weighs 3 lb., and yet it has the capacity to conceive of a universe a billion light-years across. Isn’t that marvelous" Diamond is an esteemed neuroanatomist (神经解剖学家) and one of the most admired professors at the University of California, Berkeley. It would be a privilege for anyone to sit in on her lectures. And, in fact, anyone can. Videos of her popular course are available free online, part of a growing movement by academic institutions worldwide to open their once exclusive halls to all who want to peek inside. In March,YouTube launched an education hub called YouTube Edu, dedicated exclusively to videos from the more than 100 schools--ranging from Grand Rapids Community College to Harvard Business School--that have set up official channels on the site. Liberated from the stew of pop-culture vlogs (视频博客) and silly cat videos, the collection highlights how much free education is out there. The bigger question is, why have colleges started posting all this stuff at no charge "Schools have always wanted to have their own area where they could be among their peer institutions and help with the discovery of their content," says Obadiah Greenberg,who leads the project at YouTube. The volume of YouTube Edu’s content, which includes campus tours and other nonacademic material, can be overwhelming, but the view-count sorting feature helps users quickly locate must-see videos, which they can comment on and rate on a five-star scale. There is clearly a big appetite for all kinds of online lectures. But one of the most interesting consequences of open courseware may be its impact on teachers,who have a new way to get feedback--and exposure. "It used to be that research was No. 1. Now people are working harder to be better teachers," Diamond says. Sifting through e-mails, the 82-year-old professor reads over messages she’s saved from students and teachers who watched her lectures from as far away as England and Egypt. "At this time of life, when everybody else is retiring and stepping aside, thinking they’ve done it all, you’re getting this worldwide connection. It’s beautiful.\ What is the positive influence the online video courses have on teachers
A. They can pay more attention to research. B. They can know better about students’ responses. C. They can delay their retiring time. D. They can connect worldwide teachers together.