The correct answer is option 1 - creep.

Creep refers to the extremely slow downslope movement of soil or rock fragments under the force of gravity. This movement occurs due to continual or seasonal agitation of particles.

Option 2 - earth flow, refers to a faster downslope movement of soil or rock fragments, typically due to saturation with water. This movement is characterized by a fluid-like flow.

Option 3 - saltation, refers to the movement of particles in a bouncing or hopping motion, typically seen in the transport of sand or small pebbles by wind or water.

Option 4 - solifluction, refers to the slow movement of waterlogged soil or sediment over a frozen subsurface. This is typically seen in areas with permafrost or in colder climates.

Overall, option 1 is the correct answer as it best describes the slow downslope motion of soil or rock fragments under gravity due to continual or seasonal agitation of particles.