13. In an attempt to sell radio advertising time, this ad claims that radio advertising will make businesses more profitable. The evidence cited is a ten percent increase in business that the Cumquat Cafe has experienced in the year during which it advertised on the local radio station. This argument is unconvincing because two questionable assumptions must be made for the stated evidence to support the authors conclusion.来源：考试大
The first assumption is that radio advertising alone has caused the increase in business at the Cumquat Cafe. This assumption is questionable because it overlooks a number of other factors that might have contributed to the Cumquat s success. For example, the Cumquat might have changed owners or chefs. it might have launched a coupon ad campaign in the local print media. or it might have changed or 0updated the menu. Yet another possibility is that a local competitor went out of business. These are just a few of the factors that could help explain the Cumquat s growth. Because the author fails to eliminate these possibilities, the assumption in question need not be accepted.来源：考试大
Even if it is granted that radio advertising is responsible for the Cumquat s success, another assumption must be made before we can conclude that radio advertising will result in increased profits for businesses in general. We must also assume that what is true of the Cumquat will likewise be true of most other businesses. But there are all kinds of important differences between cafes and other businesses that could affect how radio audiences react to their advertising. We cannot safely assume that because a small restaurant has benefited from radio advertising, that any and all local businesses will similarly benefit.
In conclusion, it would be imprudent for a business to invest in radio advertising solely on the basis of the evidence presented. To strengthen the conclusion, it must be established that radio advertising was the principal cause of increased business at the Cumquat. Once this is shown, it must be determined that the business in question is sufficiently like the Cumquat, and so can expect similar returns from investment in radio ad time.