A、It can hardly be heard. B、It can hardly be noticed. C、It is used everywhere. D、It changes people’s ideas. B男士说，背景音乐能够影响你的态度，调节

M: Background music is supposed to influence your attitudes and put you in the right mood. You’re not supposed to notice it, but it’s just there, in the background.
W: I’m not sure I like it.
M: Well, it does work. Factories use it a lot. It makes the workers happy, and they work better that way. In one factory, music increased production by 4.5 percent.
W: I should think they’d get tired of hearing music all day.
M: They don’t though. One fellow in Chicago told me, "If the music stops, somebody always runs to the telephone to complain."
W: Now that I think about it, I can’t remember when there wasn’t background music in restaurants.
M: Actually, background music started during World War II when some factories had their own orchestras to keep workers happy and calm. Now, the music is piped in by a machine, and different kinds of music are played at different times during the day. They play faster music at ten in the morning than at eight, for instance, because workers tend to be slower then.
W: What about restaurants? Do they play the same music for dinner and lunch?
M: I don’t know about that, but I do know that hamburger places play fast music. When they started playing faster music, they found that a customer spent less time eating.
W: So they have more people coming in and out to buy hamburgers.
M: Exactly. And that’s good for business. You can see why music has become so popular. Prisons use it, and farmers use it to keep their cattle calm. It’s even supposed to have an effect on plants.
W: Well, it may calm cattle, but it’s not making me forget—I’m hungry. Let’s get that waitress to bring us a menu.
9. What do we learn about background music from the beginning of the conversation?
10. Where was background music first used?
11. Why is fast background music played in hamburger places?