Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions (from 31 to 35). NATURE IN DANGER Deforestation has important global consequences. Forests sequester carbon in the form of wood and other biomass as the trees grow, taking up carbon dioxide from the atmosphere. When forests are burned, their carbon is returned to the atmosphere as carbon dioxide, a greenhouse gas that has the potential to alter global climate, ...

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions (from 31 to 35). NATURE IN DANGER Deforestation has important global consequences. Forests sequester carbon in the form of wood and other biomass as the trees grow, taking up carbon dioxide from the atmosphere. When forests are burned, their carbon is returned to the atmosphere as carbon dioxide, a greenhouse gas that has the potential to alter global climate, and the trees are no longer present to sequester more carbon. In addition, the effects of forest clearing, selective logging, and fires interact. Selective logging increases the flammability of the forest because it converts a closed, wetter forest into a more open, drier one. This leaves the forest vulnerable to the accidental movement of fires from cleared adjacent agricultural lands and to the killing effects of natural droughts. As wildfires, logging, and droughts continue, the forest can become progressively more open until all the trees are lost. Additionally, the burning of tropical forests is generally a seasonal phenomenon and can severely impact air quality. Record-breaking levels of air pollution have occurred in Southeast Asia as the result of burning for oil palm plantations. In the tropics, much of the deforested land exists in the form of steep mountain hillsides. The combination of steep slopes, high rainfall, and the lack of tree roots to bind the soil can lead to disastrous landslides that destroy fields, homes, and human lives. With the significant exception of the forests destroyed for the oil palm industry, many of the humid forests that have been cleared are soon abandoned as croplands or only used for low-density grazing because the soils are extremely poor in nutrients. The vegetation that contains most of the nutrients is often burned, and the nutrients literally "go up in smoke" or are washed away in the next rain. Although forests may regrow after being cleared and then abandoned, this is not always the case, especially if the remaining forests are highly fragmented. Such habitat fragmentation isolates populations of plant and animal species from each other, making it difficult to reproduce without genetic bottlenecks, and the fragments may be too small to support large or territorial animals. Furthermore, deforested lands that are planted with commercially important trees lack biodiversity and do not serve as habitats for native plants and animals, many of which are endangered species. (Source: )

The passage is mainly about _______ .