5. Đọc kỹ đoạn văn sau và chọn phương án đúng (A, B, C hoặc D) cho mỗi câu.
Probably the most important factor governing the severity of forest fires is weather. Hot, dry weather lowers the moisture content of fuels. Once a fire has started, wind is etremely ctitical because it influences the oxygen supply and the rate of spread. Forest type and forest conditions are also important factors. For example, fire is more likely to occur in conifers than in hardwoods; slash-covered or brushy areas are especially hazardous because the rate at which combustion consumes fuel is proportional to fuel volume.
Some fires are caused by lightning; others are caused by people. Those caused by people may be accidental or intentional (incendiary). The causes of fire in the United States show large regional differences. In the Rocky Mountains more than 70 percent of the fires are caused by lightning, whereas incendiary fires amount to only about 1 percent. In contrast, more than 40 percent of the fires in the South are incendiary, whereas lightning causes only 1 percent.