The correct answer is C) You should tack or jibe to the port tack and make all possible headway to the south. This is the correct answer because in the given scenario, with a dangerous shoal bearing 270° true and range 5 miles, the appropriate action is to tack or jibe to the port tack and head south to increase the distance from the shoal. This maneuver will allow the vessel to move away from the hazard as quickly as possible. The other answer choices are incorrect because: A) staying alert may not be enough to avoid the shoal, B) setting a reefed foresail and striking the jib would not provide the necessary headway to the south, and D) making way to the north would increase the risk of grounding on the shoal.