19.      
　　 Recent social changes in the country of Spiessa lead the author to predict a continued surge in growth of that country's restaurant industry. Rising personal incomes, additional leisure time, an increase in single-person households, and greater interest in gourmet¹ food are cited as the main reasons for this optimistic outlook. All of these factors are indeed relevant to growth in the restaurant industry; so the prediction appears reasonable on its face. However, three questionable² assumptions operative in this argument bear close examination.

      The first dubious³ assumption is that the supply of restaurants in Spiessa will continue to grow at the same rate as in the recent past. However, even in the most favorable conditions and the best of economic times there are just so many restaurants that a given population can accommodate and sustain. It is possible that the demand for restaurants has already been met by the unprecedented⁴ growth of the past decade, in which case the recent social changes will have little impact on the growth of the restaurant industry.

      A second assumption is that the economic and social circumstances cited by the author will actually result in more people eating out at restaurants. This assumption is unwarranted, however. For example, increased leisure time may just as likely result in more people spending more time cooking gourmet meals in their own homes. Also, single people may actually be more likely than married people to eat at home than to go out for meals. Finally, people may choose to spend their additional income in other ways—on expensive cars, travel, or larger homes.

      A third poor assumption is that, even assuming people in Spiessa will choose to spend more time and money eating out, no extrinsic⁵ factors will stifle⁶ this demand. This assumption is unwarranted. Any number of extrinsic factors—such as a downturn in the general economy or significant layoffs⁷ at Spiessa's largest businesses—may stall the current restaurant surge. Moreover, the argument fails to specify⁸ the "social changes" that have led to the current economic boom. If it turnsout these changes are politically driven, then the surge may very well reverse if political power changes hands.

      In conclusion, this argument unfairly assumes a predictable future course for both supply and demand. To strengthen the argument, the author must at the very least show that demand for new restaurants has not yet been exhausted⁹, that Spiessa can accommodate new restaurants well into the future, and that the people of Spiessa actually want to eat out more.
20.        
　　Laboratory studies show that Saluda Natural Spring Water contains several of the minerals necessary for good health and that it is completely free of bacteria. Residents of Saluda, the small town where the water is bottled, are hospitalized less frequently than the national average. Even though Saluda Natural Spring Water may seem expensive, drinking it instead of tap waster is a wise investment in good health．
 
Sample Essay 1:
      The argument that drinking Saluda Natural Spring Water instead of tap water is a wise investment in good health is not entirely¹⁰ logically convincing, since it lacks certain supporting factors.

       Firstly, the argument assumes that Saluda Natural Spring Water is the major reason why residents of Saluda are less frequently hospitalized than the national average. However, there is little evidence that this water is the only difference between this place and the rest of the country. And the reason why people in other places are more hospitalized are numerous and varied¹¹. There are so many other factors that would bring people in other places to hospitals, such as accidents, food contamination, illnesses, etc.

      Secondly¹², the argument also assumes that the minerals in Saluda National Spring Water are the key minerals for the good health of the residents of Saluda. However, this may not be true. We need not only minerals to keep good heath but also various vitamins. Besides, our body needs more minerals than those contained in Saluda Natural Spring Water.

      Finally, even if the Saluda water is the major reason why the residents of Saluda are less hospitalized, the argument still omits the fact that there is more than one way to keep drinking water free from bacteria. For instance, the most common practice is to boil water up to 100 degree Celsius¹³ and keep it at that degree for more than 5 minutes. Therefore drinking Saluda water to keep good health is not the only alternative.

      Thus, the argument is not completely sound. The evidence in support of the conclusion that the Saluda residents are less hospitalized does little to prove the conclusion-that drinking Saluda Natural Spring Water is a wise investment in good health-since it omits the assumptions I have just raised. The argument might have been strengthened by making it plain that Saluda Natural Spring Water is the major reason why the residents of Saluda are less hospitalized, that the water contains all the major minerals essential for the human body, and that there is no other way to keep water from bacteria.
 
Sample Essay 2:
      In this argument the author concludes that drinking Saluda Natural Spring Water (SNSW) is preferable to drinking tap water. Three reasons are offered in support of this conclusion: SNSW contains several of the minerals necessary for good health, it is completely tree of bacteria, and residents of Saluda—the town where it is bottled—are hospitalized less frequently than the national average. This argument is unconvincing because it relies on a variety of dubious assumptions.

      The first questionable assumption underlying¹⁴ this argument that tap water does not contain the minerals in question and is not completely free of bacteria. This assumption is not supported in the argument. If tap water is found to contain the same minerals and to be free of bacteria, the author's conclusion is substantially undermined.

      A second assumption of the argument is that the water residents of Saluda drink is the same as SNSW. Lacking evidence to the contrary, it is possible that Saluda is not the source of the bottled water but is merely the place where SNSW is bottled. No evidence is offered in the argument to dispute this possibility.

      Finally, it is assumed without argument that the reason residents are hospitalized less frequently than the national average is that they drink SNSW. Again, no evidence is offered to support this assumption. Perhaps the residents are hospitalized less frequently because they are younger than the national average, because they are all vegetarians¹⁵, or because they exercise daily. That is, there might be other reasons than the one cited to account for this disparity.

      In conclusion, this is an unconvincing argument. To strengthen the conclusion that SNSW is more healthful than tap water, the author must provide evidence that tap water contains harmful bacteria not found in SNSW. Moreover, the author must demonstrate that the residents of Saluda regularly drink the same water as SNSW and that this is why they are hospitalized less frequently than the national average.