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Group B receives an inert substance that mimics the treatment—this is the control group receiving a placebo. The description says neither participants nor researchers know assignments until the end, a hallmark of a double-blind design. Thus, Option C is correct. Option A mislabels the blinding; only the participants unaware would be single-blind, but here both sides are blind. Option B misidentifies Group B as experimental (they’re not—they receive no active drug). Option D calls it a placebo group (true), but the design is not single-blind per the prompt. On GED Science, experimental design questions test identification of independent variables (treatment), dependent variables (measured outcomes like symptom scores), control conditions (placebo), and bias-reduction methods (randomization, blinding). Double-blind procedures minimize expectancy effects from both participants and researchers and strengthen internal validity. Always read the blinding description carefully; “neither side knows” → double-blind.