Which of the following is different from the rest?

Concept: An "odd one out" item names four terms and asks which one does not share the same underlying process/category as the other three. Solve it by defining each term precisely, then checking which definitions describe the same kind of activity and which one names a different kind of activity.

Application: Deforestation, Desertification, and Erosion each name a process by which land, forest cover, or topsoil is lost or degraded — trees are cleared, fertile land turns desert-like, or soil/rock is worn away and carried off. Conservation names the opposite kind of activity: the deliberate protection and management of a natural resource so that it is maintained rather than lost. Because three of the four terms describe a loss/degradation process and only Conservation describes a protection/management process, Conservation is the term that does not belong with the rest.

Cross-check — what each term names:

Result: Conservation is different from the rest because it is a resource-protection activity, while Deforestation, Desertification, and Erosion are all resource-degradation processes. The correct option is Conservation.