(a) The Concentric Zone model was proposed by Burgess in 1925, and it depicts the US city of 1900-1950, which was expanding rapidly as people moved away from inner-city locations toward places with a higher standard of living.
(b) The CBD contains the peak land value intersection, the most expensive land in the city, because of high demand and central accessibility. As a result, land is used intensively, with a high concentration of skyscrapers and multi-story commercial buildings.
(c) As the CBD continuously expands, it pushes into the Zone in Transition, causing the surrounding zones to continually push outwards and rebuild their infrastructures. In invasion, a new or incoming group, often newer, poorer immigrants, enters an established area; in succession, the incoming group completely replaces the previous group and changes the cultural, ethnic, or socioeconomic character of the neighborhood.
(d) One criticism is that the model is America-centric. While North American cities feature poorer populations in the CBD and wealth in the outer suburbs, cities in Europe and Asia were historically built around central fortresses or palaces, so the wealthiest residents stayed in the city center rather than on the periphery. Therefore the model lacks applicability outside North America.

(a) Urban sprawl is the unrestricted, low-density expansion of housing, commercial strip malls, and roads over vast expanses of rural land with minimal centralized urban planning.
(b) Two causes of suburbanization are automobile ownership and the Interstate Highway Act of 1956 in the U.S. Larger homes, lower land costs, and government mortgage policies and zoning also contributed.
(c) One negative impact is high infrastructure costs. Extending water, power, roads, and emergency services over large, spread-out distances drains municipal budgets.
(d) One consequence for the city center is the erosion of its tax base, which leads to urban decay. Suburbanization also increased socio-economic and racial segregation (white flight).

Part A Two technological innovations associated with the Green Revolution are high-yield hybrid seeds (HYVs) engineered for higher grain density and synthetic nitrogen-based chemical fertilizers.
Part B The Green Revolution dramatically boosted global food security by exponentially increasing crop yields per acre in densely populated LDCs, which averted widespread famines and allowed countries like India to transition from food dependence to self-sufficiency in wheat production.
Part C First, Green Revolution research focused predominantly on rice, wheat, and maize, largely ignoring traditional African staple crops such as cassava, sorghum, and yams. Second, Sub-Saharan Africa lacked the necessary physical and financial infrastructure—such as transport networks, electricity, and mechanized irrigation—needed to support water- and input-intensive HYV crops.
Part D One negative environmental consequence is soil salinization caused by over-irrigation in arid regions. As heavy irrigation water rapidly evaporates under intense heat, dissolved mineral salts build up on the soil surface, rendering farmland toxic to future crops.
Part E Small-scale farmers in LDCs face high capital barriers because Green Revolution technologies require annual purchases of expensive patented seeds, synthetic chemicals, and fuel. Without access to affordable credit or government subsidies, these high input costs often force smallholders into severe debt.