The correct answer is B) heaving line. A monkey fist is a type of knot that is commonly found on the end of a heaving line, which is a lightweight line used to throw a heavier line (such as a mooring line) to another vessel or a dock. The monkey fist allows the heaving line to be thrown further and with more accuracy. The other options are incorrect because a monkey fist would not typically be found on a manrope (a line used to assist in boarding a vessel), a mooring line (a line used to secure a vessel to a dock), or a lead line (a line used to measure the depth of water).