听力原文： When you see a clever advertisement in a newspaper, do you say to yourself, 'Ah, that's good. I'd like to have one of those'? Or do you say, 'What lies are they telling this time? It can't be very good or they wouldn't have to advertise it so cleverly'? Both of these people exist the first are optimists the second, pessimists and realists. Advertisements can be extremely useful if they are honest if, let us say, you have broken your pen and you want to buy another, the first thing to do is to look at as many advertisements for pens as you can find. That will help you to choose the model, color and price that suit you. Advertisements save a lot of time and trouble by putting sellers in touch with buyers in a quick and simple way. If the advertisements are true and accurate, the customers will be satisfied and will probably buy from the same firm next time and advise their friends and acquaintances to do the same. The really dishonest advertiser hopes to sell his goods quickly and to make a large profit on them before the customer's reactions begin. He knows that no customers will buy from him a second time, and that none will recommend his products to their friends. But there are also semi-dishonest advertisers. They make claims for their products which they know perfectly well to be incapable of verification, like advertising that a certain toothpaste contains a particular substance—which it in fact does—knowing that this substance is in fact neither beneficial nor harmful to the teeth. Such advertisements do not tell downright lies, but their advertising is deliberately misleading. (30)