Final answer:
In the itching powder experiment, neither Subject A nor Subject B serves as a control group because both are exposed to some form of itching powder. A proper control group would receive a placebo, which neither of these subjects did. The correct answer is d. Neither A nor B.
Step-by-step explanation:
The control group in an experiment is the group that receives an inactive treatment but is otherwise managed exactly as the other groups. This helps to isolate the effect of the treatment variable by providing a baseline for comparison.
In the case of an itching powder experiment, the control group would be the one that does not receive the active itching powder, ensuring that any difference in itching sensation between the groups can be attributed to the active ingredient in the experimental itching powder.
Given the options provided for the itching powder experiment, neither A nor B serves as a control group since both groups receive a form of itching powder.
A true control group would require a substance that looks like the itching powder but has no active effect, such as a placebo. Therefore, the correct answer is d. Neither A nor B.