The correct answer is C) running fix. A running fix is a position obtained by taking lines of position from one object at different times and then advancing them to a common time. This allows the mariner to determine their position relative to that single object at a specific time. This is in contrast to a fix, which is a position determined by taking lines of position from two or more objects at the same time. The other answer choices are incorrect because: A) Dead-reckoning is the process of estimating one's current position based on a known previous position, course, and speed. B) Estimated position is a position determined by consideration of all available information, but without the accuracy of a fix. D) A fix is a position determined by taking lines of position from two or more objects at the same time.