How does a double-blind experiment work?

Correct Answer: B

Rationale: The correct answer is B. In a double-blind experiment, neither the subjects nor the researchers know which subjects are in the control or experimental group. This helps to eliminate bias and ensure that the results are more objective. Choice A is incorrect as in a double-blind experiment, subjects do not take turns receiving each treatment; it is about masking the treatment allocation. Choice C is incorrect because it implies that the researchers are aware of the group allocation, which goes against the principle of blinding in a double-blind study. Choice D is incorrect as both subject groups should not know whether they are in the control or experimental group to maintain the blindness of the study.

Correct Answer: C

Rationale: When an increase in exercise is accompanied by a decrease in body weight, it demonstrates a negative correlation. This means that as one variable (exercise) increases, the other variable (body weight) decreases. Choice A, 'variable effect,' is vague and does not accurately describe the relationship between exercise and body weight. Choice B, 'positive correlation,' is incorrect because in a positive correlation, both variables would increase or decrease together. Choice D, 'randomization effect,' is unrelated to the scenario described.

Correct Answer: D

Rationale: The Recommended Dietary Allowances (RDAs) are the best measure to describe the amounts of nutrients that should be consumed by the population. RDAs represent the average daily intake level that meets the nutrient requirements of nearly all (97-98%) healthy individuals in a particular life stage and gender group. Choice A, the Dietary Reference Intakes, provide a set of nutrient intake values but do not specifically address the average daily amount of a nutrient considered adequate for practically all individuals. Choice B, the Tolerable Upper Intake levels, focus on the maximum daily amount of a nutrient deemed safe for most healthy people, not the average daily amount needed. Choice C, the Estimated Average Requirements, reflect the average daily amount of a nutrient needed by half of the healthy individuals, which is not as comprehensive as the RDAs that cater to nearly all healthy people.

Correct Answer: D

Rationale: The correct answer is D. A placebo serves as a control for comparison with the treatment group, helping to eliminate bias and ensure the results are due to the treatment itself. Placebos are crucial in research to distinguish the actual effect of the treatment from psychological or subjective factors. Choice A is incorrect because the purpose of a placebo is not related to reducing the cost of the experiment. Choice B is incorrect because while placebos are used in double-blind studies, their primary purpose is not to make the experiment double-blind. Choice C is incorrect because the purpose of a placebo is not to increase the number of participants but rather to serve as a comparison group for the treatment being tested.

Correct Answer: D

Rationale: Glucose is the correct answer as it is the primary source of energy for the brain and nervous system. The brain relies heavily on glucose to function optimally. While protein and fat play essential roles in the body, they are not the primary sources of energy for the brain and nervous system. Carbohydrates, on the other hand, are broken down into glucose, which is then used as fuel by the brain and nervous system.