Câu hỏi:

Read the following passage and mark the letter A, B, C or D on your answer sheet to choose the word or phrase that best fits each other numbered blanks. 

     Trees protect the soil beneath them; thus, tree loss can affect soil integrity. For example, the rain forest floor, home to numerous plant life as well as insects, worms, reptiles and amphibians, and small mammals, relies on a dense covering of branches and leaves to keep it healthy and intact. The canopy of leaves prevents surface runoff by (4) ________ heavy rainfall, so that water can drip down slowly onto the porous earth. Tree roots also stabilize the soil and help prevent erosion. In return, a healthy soil encourages root development and microbial activity, (5) ________ contribute to tree growth and wellbeing. A major factor in cutting forest -related soil damage comes (6) ________ road building, with trucks and other heavy equipment compressing the soft soil, creating furrows where water collects, and disrupting the underground water flow. Eventually, the topsoil erodes, leaving behind (7) ________ infertile layer of rocks and hard clay. 

     Logging can also damage aquatic habitats. Vegetation along rivers and stream banks helps maintain a steady water flow by blocking the entry of soil and other residue, and trees shade inhibits the growth of algae. Removing trees (8) ________ these benefits. When eroding soil flows into waterways, the organic matter within it consumes more oxygen, which can lead to oxygen depletion in the water, killing fish and other aquatic wildlife.