The correct answer is C because the main legal risk in a consent-based search is exceeding the permission that was actually granted. For that reason, the consent documentation must clearly define the scope of what systems may be searched, what actions are permitted, and what evidence may be seized or examined. CHFI v11 includes seeking consent, search and seizure, and best practices for handling digital evidence, so candidates are expected to recognize that detailed scope control is what keeps the search lawful and defensible. Formal documentation is important, and valid authority to consent also matters, but neither addresses the specific problem in the question as directly as a clearly defined scope. In digital investigations, devices and systems often contain far more data than is relevant, so ambiguity in consent can quickly create legal problems. Since the question asks what requirement best prevents investigators from going beyond the authorized boundaries, the strongest answer is that the consent must clearly outline the scope of permitted search and seizure activities.