The sudden rapid movement of an unsaturated cohesive mass of soil, regolith, or bedrock is a The sudden rapid movement of an unsaturated cohesive mass of soil, regolith, or bedrock is a: a) debris avalanche.
b) mudflow.
c) landslide.
d) rockfall.

The correct option is C: landslide

Explanation:

A landslide is a huge amount of land, rocks, and other materials that moves downhill. These land moves are caused by erosion and other strengths that may cause the land to move and fall from a steep hillside. Erosion might cause separation of different material layers, and when a land o rocky layer is separated from its immediately anterior one, gravity causes the fall of these layers.

In general, these land moves are very destructive. They can cover rivers, routs, buildings, among others, putting in danger any kind of life.  

There are other moves very similar to landslides, such as mudflow, avalanche, or rockfall.

Rockfall refers to the fall or big rocks from a precipice or steep hillside.

Mudflow refers to a thick stream of mud and other materials.

Avalanche refers to the collapse of snow and other materials.

d. planting trees

the trees take in carbon to make oxygen.