No person may serve as the person in charge of oil transfer operations on more than one vessel at a time __________.

Correct Answer: Option C — unless authorized by the captain of the port

33 CFR 155.700 prohibits a person from serving as the Person in Charge (PIC) of oil transfer operations on more than one vessel simultaneously. This regulation ensures undivided attention to the critical safety and environmental aspects of the transfer, unless specific authorization is granted by the local Captain of the Port.