Advertisement: Do you want to be more energetic and physically fit? Take a daily supplement of Vita-Plus, a vitamin combination containing additional proprietary ingredients. Our Study using hundreds of volunteers show that just after 1 week of taking 2 capsules daily, participants report being more energetic and alert on average than the average level reported by national institute of health survey of all Americans

Which of the following will most strengthen the advertisements claim that vita-plus supplements make one more energetic and alert.

1) Those who voluntarily choose to take 2 capsules daily reported energy levels even greater than those who took only 2 capsules
2) The volunteers were randomly selected from all those who a newspaper advertisement and were willing to pay for the cost of Vita Plus capsules
3) At the beginning of the study, the volunteers' reports on alertness showed levels on average no different from the average level reported by National institute of health.
4) Some of the volunteers were given capsules that solely contained cellulose, an inert substance with no vitamins or health inducing substance. Those volunteers also reported increased levels of alertness and energy
5) 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


I think the answer should be 3 but the official answer is 5. Can somebody explain why?