Passage One Questions 21 to 25 are based on the following passage. The appeal of advertising to buying motives can have both negative and positive effects. Consumers may be convinced to buy a product of poor quality or high price because of an advertisement. For example, some advertisement have appealed to people's desire for better fuel economy for their cars by advertising automotive products that improve gasoline mileage. Some of the products work. Others are worthless and a waste of consumers' money. Sometimes advertising is intentionally misleading. A few years ago, a brand of bread was offered to dieters(节食者)with the message that there were fewer calories(热量单位, 卡)in every slice. It turned out that the bread was not dietetic(适合于节食的), but just regular bread. There were fewer calories because it was sliced very thin. but there were the same number of calories in every loaf. On the positive side, emotional appeals may respond to a consumer's real concerns. Consider fire insurance. Fire insurance may be sold by appealing to fear of loss. But fear of loss is the real reason for fire insurance. The security of knowing that property is protected by insurance makes the purchase of fire insurance a worthwhile investment for most people. If consumers consider the quality of the insurance plans as well as the message in the ads, they will benefit from the advertising. Each consumer must evaluate her or his own situation. Are the benefits of the product important enough to justify buying it? Advertising is intended to appeal to consumers, but it does not force them to buy the product. Consumer still controls the final buying decision. Advertising can persuade the consumer to buy worthless product by______.