When land has been overfarmed or overgrazed, occurs.
a. wasteland
b. deforestation
c. desertification
d. underdevelopment

The best option is C. desertification.

When land has been over farmed or overgrazed , desertification occurs.

Desertification is said to be a process  of degradation of land whereby land that was previously biologically productive is changed into a barren, unproductive land.

Desertification can be brought about by poor use  and destruction of natural resources such forest and natural vegetation. Such include:

1. Excessive tree felling or cutting

2. Unsustainable farming practices  which lead to loss of soil fertility.

3. Removal of vegetation cover.

4. overgrazing.

5. Uncontrolled fuel wood gathering  or collection.

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.