First Principles Thinking: fund manager's duty runs to the mandate
A is correct. Where a member manages a fund to an index or an expected mandate, the CFA Curriculum places the duty of loyalty, prudence, and care on investing consistently with the stated mandate. Decisions benefit all fund investors collectively and are not made on the basis of any individual investor's requirements or risk profile. Client loyalty and care for the individual investor rest with any adviser who has an advisory relationship with that investor.
B overreaches. Pereira still owes a duty of loyalty, prudence, and care, but it is owed through the vehicle of the fund mandate rather than to each investor as an advisory client.
C inverts the CFA Curriculum by transplanting individual advisory duties onto a fund manager, which would make coherent fund management impossible and is not supported by the standard.