The correct answer is D) Fix. A fix is an accurate position that is not based on any prior position. It is determined by taking a visual, electronic, or other observation and using it to plot the vessel's precise location on a chart. This is the most accurate method of determining a vessel's position, as it does not rely on estimations or calculations from previous positions. The other options are incorrect because: A) Dead-reckoning position is an estimate of the vessel's position based on course, speed, and time traveled from a known position. B) Estimated position is a position that is based on other position information, such as a previously determined fix or a running fix. C) Running fix is a position determined by taking two or more observations over time and plotting the vessel's position based on the intersection of the lines of position.