Which term describes a reference point whose elevation is known and marked?

The correct choice is "C. Bench Mark." A bench mark is a specific point of known elevation, which serves as a reference for surveying and construction activities. These markers are critical in establishing a consistent frame of reference when measuring changes in elevation across different locations. They can be natural features or artificial structures that have been accurately surveyed and documented.

Bench marks play a vital role in ensuring accuracy in various engineering and construction projects, as they provide a reliable point from which heights and depths can be calculated. This is especially important when laying the foundation for buildings, roads, or other infrastructure, where precise elevation measurements are crucial for stability and design integrity.