The correct answer is A) shift your rudder. During a Williamson turn, which is a maneuver used to quickly turn the vessel around to retrieve a person who has fallen overboard, you should shift the rudder to counter the swing of the vessel and help it complete the turn. Keeping the rudder amidships during the turn would not provide enough control to effectively complete the maneuver. The other options are incorrect because: B) putting the rudder amidships would not provide enough rudder to complete the turn, C) stopping the engines is not necessary during a Williamson turn, and D) increasing to maximum speed is not the appropriate action for this specific maneuver.