7. 
　　 In this argument the author concludes that people trying to lose weight are better off consuming sugar than the artificial sweetener aspartame. To support this conclusion the author argues that aspartame can cause weight gain by triggering food cravings, whereas sugar actually enhances the body's ability to bum fat. Neither of these reasons provides sufficient support for the conclusion.
来源：考试大
      The first reason that aspartame encourages food cravings is supported by research findings that high level s of aspartame deplete the brain chemical responsible for registering a sense of being sated, or full. But the author's generalization based on this research is unreliable. The research was based on a sample in which large amounts of aspartame were administered; however, the author applies the research findings to s target population that includes all aspartame users, many of whom would probably not consume high levels of the artificial sweetener.
来源：考试大
      The second reason that sugar enhances the body's ability to bum fat is based on the studies in which experimental groups, whose members consumed sugar after at least 45 minutes of continuous exercise, showed increased rates of fat burning. The author's general claim, however, applies to all dieters who use sugar instead of aspartame, not just to those who use sugar after long periods of exercise. Once again, the author's generalization is unreliable because it is based on a sample that clearly does not represent all dieters.
来源：考试大
      To conclude, each of the studies cited by the author bases its findings on evidence that does not represent dieters in general; for this reason, neither premise of this argument is a reliable generalization. Consequently, I am not convinced that dieters are better off consuming sugar instead of aspartame.