Explanation: The Distance Measuring Equipment (DME) system uses radio signals to determine the actual line-of-sight distance between an aircraft and a ground transponder. Because the aircraft is typically at some altitude above the ground station, this measured distance is the hypotenuse of a right triangle, not the horizontal distance over the ground. This direct, line-of-sight distance is precisely what is referred to as the **slant range**. It represents the true distance the radio signal travels. The other options are incorrect: * **A) DME bearing:** DME provides distance, not bearing (direction). Bearing is typically provided by a VOR (VHF Omnidirectional Range) station. * **C) Glide Slope angle of approach:** Glide slope is part of an Instrument Landing System (ILS) and provides vertical guidance (an angle) for descent, separate from DME's distance measurement. * **D) Localizer course width:** Localizer, also part of ILS, provides horizontal guidance (a course width or deviation) to align with a runway, not a distance.