The correct answer is A) stopper. The stopper knot is a simple knot used to prevent the end of a line from passing through a hole or opening. This type of knot is commonly used in applications where you need to secure the end of a line, such as on the Coast Guard Captain's License Examination. The illustration D030DG clearly shows a stopper knot, which is indicated by the letter "N" in the image. The other answer choices are incorrect because they do not match the knot shown in the illustration. A rolling bowline, heaving line hitch, and timber hitch have different structures and are used for different purposes than a stopper knot.