题目:
Advertisement: Do you want to be more energetic, vigorous, and physically fit? Take a daily supplement of Vita-plus, a vitamin combination containing additional proprietary ingredients. Our studies using hundreds of volunteers show that after just one week of taking 2 capsules daily, participants report being more energetic and alert on average than the average level reported by the National Institutes of Health survey of all Americans.
Which of the following would most strengthen the advertisement’s claim that Vita-Plus supplements make one more energetic and alert?
选项:
A、A. Those who voluntarily chose to take more than 2 capsules daily reported energy levels even greater than those who took only 2 capsules.
B、B. The volunteers were randomly selected from all those who answered a newspaper advertisement and were willing to pay for the cost of the Vita-Plus capsules.
C、C. At the beginning of the study, the volunteers' reports on alertness showed levels on average no different from the average level reported by the National Institutes of Health.
D、D. Some of the volunteers were given capsules that solely contained cellulose, an inert substance with no vitamins or other health-inducing substances. Those volunteers also reported increased levels of alertness and energy.
E、E. Some of the volunteers were given capsules that solely contained cellulose, an inert substance with no vitamins or other health-inducing substances. Those volunteers reported no increase in alertness or energy.
答案:
E