Which kind of ground cover fire is slow moving and smoldering?

The correct answer focuses on ground fire, which is characterized by its slow-moving and smoldering nature. Ground fires burn below the surface, primarily in the organic material in the soil, such as peat or decomposed vegetation. This type of fire does not spread rapidly like surface or crown fires; instead, it can burn quietly for extended periods, often undetected, making it a significant threat, particularly in forested areas with heavy leaf litter or in peat bogs.

Surface fires typically burn the vegetation above ground, often spreading more quickly and intensely. Crown fires can be extremely destructive as they spread through the tops of trees, fueled by the canopy and often moving at a high rate of speed. The term "hot fire" is not a specific classification in firefighting terminology and may suggest intensity without clarity on the behavior or type of fire. Therefore, ground fire is the most fitting choice for the characteristics described in the question.