Which statement best describes the process of desertification? a. desert areas expand into areas that had previously been fertile. b. desert areas are created after extensive flooding occurs. c. many people move to the desert for economic opportunities. d. forests expand into areas that had been deserts.

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

The cretaceous period spanned the time interval between and 65 million years ago. 250 million 144 million 75 million 200 million

Match each medication with its description.