Select the response that is true

a$.$ For confirmations sent by mail, the auditor must maintain control of the confirmations until they are returned from the customer. The auditor must also mail the confirmations outside of the client's office.

b$.$ For confirmations sent by mail, the auditor must maintain control of the confirmations until they are returned from the customer. The auditor can mail the confirmations from any Postal Service location or drop box.

c$.$ The auditor should perform procedures to verify a customer's address only when the customer uses a P$.$O$.$ Box.

d$.$ The auditor should include the customer's balance on aln types of confirmation sent to the customer.