A、It started at a time when the workers were slower in work. B、it started during the Second World War. C、It started before the f

W: Howard, what are you working on now?
M: I have just finished a piece on the background music.
W: Background music? Oh, like the music they’re playing here now.
M: Yes. You can hear it everywhere-- in restaurants, airports, supermarkets, department stores and so on. It’s supposed to influence your attitudes, put you in the right mood.
W: I am not sure I like that idea.
M: Well, it seems to work. Companies pay millions of dollars every year for background music. It’s supposed to give you a better feeling about yourself and the people around you. Factories use it a lot. It makes the workers happy, and they work better that way. In one factory, music increased production 4.5 percent.
W: I should think they’d get tired of hearing music all day.
M: They don’t, though. One fellow in San Francisco 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 and stores.
M: That shows how young you are. Actually, it all started during World War Ⅱ when some factories had their own orchestras to keep workers happy and calm. Now different kinds of music are playing 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 only seventeen minutes eating. The time was twenty-minutes before that.