Which One of the Following Procedures Would Be Considered Improper

Which one of the following procedures would be considered improper for an auditor in the process of confirming receivables?

A) The auditor allows the client's staff to prepare the confirmation letters after the auditor has chosen the items to be confirmed.
B) The auditor allows the client to sign the confirmations after they are prepared.
C) The auditor allows the client's staff to mail the confirmation letters after he or she has proofed the typing of the letters.
D) The auditor asks the addressee to return the confirmation to the audit firm's office.