A、He sings a song while they dance. B、He gives orders by sing a folk song. C、He usually makes it into a song. D、He usually do it

W: Why don’t you have folk dances in the United States? Most countries have special dances that the people have done for many years. The dancers wear clothes from the old days. Everyone likes to watch them dance.
M: We have folk dances, too. A lot of people belong to folk dancing groups. But when they dance, they usually do it just to enjoy themselves. They don’t invite other people to watch them.
W: Is there a folk dancing group here?
M: I think so. There’s one in almost every city, and some big cities have several.
W: What are the dances like?
M: Usually eight people dance together, four men and four women. When they start, they form a square, with a man and a woman on each side of the square. That’s why it’s called square dancing. Then there’s a man who tells the dancers what they should do. He usually makes it into a song, and sings it while they dance.
W: Oh, that should make the dances easy!
M: Yes, but they are very fast. They don’t have much time to think. I like to watch them, though. The dancers wear old-fashioned clothes. They makes the dances pretty to watch.
W: I’d like to watch a group dance.
M: I’ll take you sometime.
Questions 16-20 are based on the passage you have just heard.
16. What is the difference between the folk dance in the US and other countries?
17. How many dancers are there in a folk dance in the US according to the man?
18. Why is it called square dance?
19. How does the man tell the dancers what they should do?
20. What kind of clothes do people wear in folk dancing?