Choice "B" is correct. The letter of inquiry to the client's attorneys is a request made by client management. Due to attorney-client privilege, the attorney would not be able to respond to such a request made by any other party. Note that management would request the attorney to respond directly to the auditor.
Choice "d" is incorrect. The auditor may request that the client include certain matters in the letter, but technically speaking, the request itself comes from client management.
Choice "c" is incorrect. The stockholders would not have any involvement in the letter of audit inquiry.
Choice "a" is incorrect. The auditor's attorney would not have any involvement in the letter of audit inquiry related to specific client engagements.