When we think of desertification, we first think about prolonged drought conditions. Desertification can also be the result of degradation of the soil in an area as the most recent definition includes the permanent loss of fertility in an area. All of the choices below result in soil degradation leading to
desertification EXCEPT
A) The buildup of salts in irrigated soils due to evaporation.
B) The presence of rocky fields that have been tilled but not planted.
C) Overfarming or drought can change the soil so that rain no longer penetrates
D) Deforestation results in erosion: nutrient-rich top soil blows or washes away.

1. emigration the movement of people from one place to another 2. immigration a situation in which resources are being used up at a faster rate than they can be replenished 3. migration the leaving of one's homeland to settle in a new place 4. overpopulation the movement of people to a new country 5. sustainable development a situation in which the birth rate is not sufficient to replace the existing population 6. underpopulation the ability to meet current needs without reducing the ability to meet future needs 7. unsustainable development the increase in the population of a city 8. urbanization a situation in which the number of people exceeds the available natural resources in an area

Plants consume most of their carbon from a. the soil b. the water c. the roots d. the air

The vaccine in a flu shot contains weakened flu viruses. how does a flu shot work with the immune system? a. it destroys lymphocytes. b. it destroys macrophages. c. it activates macrophages. d. it activates lymphocytes.