The correct answer is D) estimated position. An estimated position is the result of combining a single line of position (such as a bearing or range to a known object) with a dead-reckoning position. This provides a more accurate position estimate than the dead-reckoning position alone, but is less precise than a true fix obtained from multiple lines of position. The other options are incorrect: A) A running fix requires two or more lines of position over time to determine a vessel's course and speed. B) A fix requires at least two intersecting lines of position to pinpoint the vessel's exact location. C) An assumed position is a position that is estimated without any new position information.