Recorded background music first found its way into factories, shops and restaurants in the States. But it soon spread to other parts of the world. Now it is becoming increasingly difficult to go shopping or eat a meal without listening to music. The best-known supplier of background music is an American company called 'Muzak'. This word also refers to recorded background music played continuously in restaurants, places of work, etc. The company has carded over a hundred studies which show that background music can create a pleasant atmosphere and improve productivity (生产效率). It must be used in the right way, though. If the type of 'Muzak' is wrong, it may well cause an entire factory to sleep! Which of the following statements is true?