The correct answer is C) Length between perpendiculars. The length between perpendiculars (LBP) is the term that indicates the length measured along the summer load line from the intersection of that load line with the foreside of the stem to the intersection of that load line with the aft side of the rudder post. This is a standard measurement used in ship design and naval architecture to define the overall length of a vessel. The other options are incorrect because they refer to different length measurements that are not specifically defined by the intersection of the summer load line and the stem/rudder post. For example, length on the waterline and length overall are different ways of measuring a ship's length that do not necessarily correspond to the LBP.