What constitutes a turning point in surveying?

Answer: B — reliable point for determining elevation

A turning point in surveying is recognized as a reliable point used for determining elevation. This point is crucial because it serves as an intermediate reference that allows surveyors to establish and maintain a consistent vertical control throughout their work. When leveling, surveyors often take a back sight on a benchmark or other established point to determine the height of the instrument. The turning point comes into play as a point where a new line of sight can be established after measuring to another point, ensuring that elevation data remains accurate over distances. The reliability of the turning point also means it should be stable and well-defined, helping to minimize errors in readings. By using it to connect various parts of a survey, or to transition between different sections, it aids in creating an accurate topographical picture of the area surveyed. This highlights why it is fundamental in the context of elevation determination within surveying.