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gFOBT detects peroxidase activity; dietary and medication interferences can cause false positives or negatives. Standard instructions include avoiding red meat (animal peroxidases), certain raw vegetables (peroxidase activity), and high-dose vitamin C (reduces color development, causing false negatives) for ~3 days before and during collection. NSAIDs can cause GI bleeding and false positives; clinicians may advise temporary avoidance if safe. Typically, samples from two areas of each of three separate bowel movements are applied to the card on different days for better sensitivity. Option B summarizes these requirements. Option A describes FIT, not gFOBT. Iron supplements (Option C) are unnecessary and can darken stool, confusing interpretation. Adding water (Option D) dilutes and contaminates the specimen. Accurate prep and collection reduce recollects and inappropriate referrals for colonoscopy—core non-blood specimen competencies.