Answer D is correct. When Claude introduces facts that are absent from the supplied source, the most directly indicated prompt defect is the absence of an explicit grounding constraint. The prompt should clearly instruct Claude to use only the supplied material, avoid relying on external or general knowledge, and state when the source does not contain enough information. It can also require supporting quotations or citations for factual claims so that unsupported additions can be detected and removed.

Option A identifies a possible contributing factor, but asking for a comprehensive response does not inherently authorize invented information. A properly constrained comprehensive response can remain fully grounded in the source. Option B is incorrect because assigning a researcher role does not necessarily produce unsupported claims; the scope and permitted sources determine the behavior. Option C is also possible in a poorly designed template, but the presence of headings alone does not explain why Claude treats unsupported content as factual.

Anthropic specifically recommends external-knowledge restrictions, direct quotations, citations, and permission to acknowledge insufficient information when reducing hallucinations. Therefore, the missing source-only constraint is the clearest root cause and should be corrected first. Anthropic: Reduce hallucinations

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