First Principles Thinking: governing standard
A is correct. The governing standard is preservation of confidentiality, while the competing principle is the duty to protect a potentially vulnerable client when warning signs of diminished capacity appear. The CFA Curriculum resolves that tension by endorsing a designated secondary contact established at the start of the relationship and allowing limited disclosures, where legally permissible, to protect the client. Here, the client previously authorized contact with the designated person, the adviser's concern is grounded in a pattern of confusion and a sudden high-risk instruction, and the adviser documents the basis for disclosure. On those facts, the conduct is not a violation of Standard III(E).
Why top distractor is tempting but wrong (missed nuance). B is tempting because acting promptly on client instructions often reflects loyalty, but the CFA Curriculum recognizes that vulnerability concerns may justify limited protective action before execution.
Why remaining distractor fails (boundary violation). C fails because the prior authorization and the narrow protective purpose place this disclosure within a recognized boundary rather than outside it.