Under which conditions would the HMMWV be operated in High/Low Range?

The correct choice highlights that the HMMWV operates in High/Low Range specifically under challenging environmental conditions such as mud, loose sand, snow, or ice. This capability is crucial as it allows for better traction and control in situations where surfaces may be slippery or unstable. When encountering these kinds of terrains, using Low Range provides the driver with increased torque and traction, enhancing the vehicle's ability to navigate through or over obstacles that would impede progress in standard High Range.

In contrast, flat terrain and well-paved roads do not typically necessitate the strategic use of High/Low Range since the HMMWV can operate efficiently and safely under normal driving conditions without needing the additional traction or power control that Low Range provides. Similarly, while steep hills or downgrades may influence driving decisions regarding speed and brake control, they do not encompass the broader range of challenging conditions represented by mud, sand, and ice, where the HMMWV's Low Range feature is particularly beneficial.