Final answer:
Creep is the most gradual form of mass movement, occurring over years and under the influence of gravity and other factors like soil saturation.
Step-by-step explanation:
The type of mass movement that takes place most gradually is c) Creep. Creep refers to the very slow movement of soil and rock down a gentle slope and can be triggered by factors such as soil saturation, freeze-thaw cycles, and the gravity acting on the slope over time. Unlike rockslides, debris flows, and mudflows that can occur more suddenly and with greater speed and force, creep is a much slower process that can continue for years without being immediately apparent. The type of mass movement that takes place most gradually is creep. Creep is a slow downslope movement of soil and regolith due to the expansion and contraction of particles caused by freeze-thaw cycles or wet-dry cycles. Over time, creep can cause fences, trees, and utility poles to tilt.