Final answer:
A certified letter marked "Confidential" should be delivered directly to the physician unopened due to the importance of maintaining privacy and security, especially in medical contexts.
Step-by-step explanation:
A piece of incoming mail that should be delivered directly to the physician unopened is b. A certified letter marked "Confidential".
Certified mail is a special service offered by mail services that provides the sender with a mailing receipt and electronic verification that the mail was delivered or that a delivery attempt was made. Handling confidential communications appropriately is crucial in maintaining privacy and security, especially in medical contexts. Therefore, any correspondence marked as confidential, particularly if it is sent via certified mail, should be delivered unopened to the intended recipient, in this case, the physician.