Final answer:
The slowest and least perceptible form of mass wasting is B) creep, where soil gradually moves down a slope due to gravity, often influenced by environmental factors like freeze-thaw cycles.
Step-by-step explanation:
The slowest and least perceptible form of mass wasting is B) creep. This type of ground movement is so gradual that changes are often difficult to detect without precise measuring instruments. Creep happens as the upper part of the soil layer gradually moves down a slope, driven by gravity. Environmental factors, such as freeze-thaw cycles, contribute to this process by expanding the soil when it is wet and contracting it when dry. As portrayed in the reference to soil terraces, when the ground is frosty, the moisture in the soil freezes and the soil expands. Once thawed, the soil subsides vertically, and these minute adjustments lead to the phenomenon of creep. Unlike more dramatic and sudden forms of mass wasting like landslides and mudflows, creep does not lead to rapid changes in the land surface.