The correct answer is D) a towing bridle. Inflatable liferafts are required to be equipped with a towing bridle, which is a line or set of lines that can be used to tow the liferaft from the water. This is an important safety feature that allows the liferaft to be maneuvered and towed to a safe location if needed. The other answer choices are incorrect because they do not accurately reflect the standard safety equipment required for inflatable liferafts. A portable radio, an oil lantern, and canned milk are not part of the mandatory liferaft equipment specified by the US Coast Guard regulations.