A、Because it is related with pop songs. B、Because it is both simple and inexpensive. C、Because you don’t need a master to teach

The podcast revolution is erupting all over the world—and seemingly all at once. [19]Why is it getting so popular? The technology is simple to master and podcasting software is inexpensive, sometimes even free. Two Chinese students are receiving international fame as millions of people around the world watch them podcast from their dormitory. They are called the Back Dormitory Boys, and they specialize in mouthing Backstreet Boys’ songs. Although most people in China don’t have iPods, podcasting is sweeping the country. [20]The Back Dormitory Boys are among the thousands of Chinese who are putting their own homemade audio and video up on the Internet for all to enjoy. "You just gotta love two guys making a fool of themselves, and gaining international attention," said "Good Morning America" technology expert Becky Worley. The Internet is becoming more and more popular with China’s youth: about 60 percent of the 100 million Chinese who use the Internet are under the age of 24. "This generation grew up with values that are very, very similar to their peers in the United States," said Huang Hung, publisher of Time Out Beijing. "You’re going to see a complete change in the cultural landscape of China." Already, podcasting has taken off in the United States. Earlier this year, 19-year-old Gary Brolsma skyrocketed to Internet fame with what he calls his "Numa Numa" dance—a lip sync to a Romanian pop song.
19. Why is podcasting sweeping the world?
20. What does podcasting mean according to the speaker?
21. Why does the speaker hold that the Internet is very popular among young people in China?