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Câu hỏi: Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer for each of the questions from 35 to 42.
Sinkholes may occur slowly and be completely harmless or may happen quickly and cause devastating damage. It is interesting that sinkholes may be caused by two opposite conditions - extreme drought or too much rain.
As depicted in the drawing, under the sandy surface soil is a layer of clay and then a layer of limestone. Sinkholes generally occur only in areas where the geology has this composition. Within the limestone areas are pockets of water and air. When the underground aquifer is full of ground water, the pockets are generally filled with water and perhaps air above the water. But when there is too much rain or not enough rain, the caverns may become unstable. When there is too much water the cavern walls can be broken because of excess pressure, and when there is too little water, the cavern walls can collapse because there is not enough internal pressure to withstand the weight from above. When that occurs, the cavern collapses, and the sandy soil close to the surface seeps or pours into the cavern. The speed of the collapse and amount of damage depends on the size of the collapsing cavern.
In drought conditions, sinkholes become more common over time. They may appear, harmlessly,in a lawn and then stop. Sometimes, small sinkholes recur or continue to eat soil for years without damage. At other times they middle of streetssurprising swallowing cars. Or they occur areas, swallowing houses. Sinkholes are not discriminating. They have swallowed small inexpensive homes, as well as huge homes worth millions of dollars. It is very rare for people to be hurt when sinkholesoccur, because theyusually happenover some time and arenoisy as the ground becomes unstable.
Sinkholes have also swallowed lakes. There are areas in Florida where 40 or more homes had been built around a beautiful lake. One day an entire lake disappeared because the cavern beneath the ground opened. Instead of sand being above the cavern, there was lake water, which flowed into the cavern, leaving behind dead and dying fish and plants and docks that led to nowhere. In one neighborhood, the neighbors managed to plug the hole in the lake with a huge block of concrete, and rain eventually filled the lake. But their efforts were to no avail because several years later the lake disappeared again.
Sinkholes are a natural phenomenon caused in particular geological areas by particular events. Unfortunately, even knowing the cause and having time to plan, it is not possible to stop a sinkhole.
The author indicates that the layers of material in soil from the top down are
A. surface, limestone, clay, and sand
B. surface, clay, sand, and limestone
C. surface, limestone, sand, and clay
D. surface, sand, clay, and limestone
Sinkholes may occur slowly and be completely harmless or may happen quickly and cause devastating damage. It is interesting that sinkholes may be caused by two opposite conditions - extreme drought or too much rain.
As depicted in the drawing, under the sandy surface soil is a layer of clay and then a layer of limestone. Sinkholes generally occur only in areas where the geology has this composition. Within the limestone areas are pockets of water and air. When the underground aquifer is full of ground water, the pockets are generally filled with water and perhaps air above the water. But when there is too much rain or not enough rain, the caverns may become unstable. When there is too much water the cavern walls can be broken because of excess pressure, and when there is too little water, the cavern walls can collapse because there is not enough internal pressure to withstand the weight from above. When that occurs, the cavern collapses, and the sandy soil close to the surface seeps or pours into the cavern. The speed of the collapse and amount of damage depends on the size of the collapsing cavern.
In drought conditions, sinkholes become more common over time. They may appear, harmlessly,in a lawn and then stop. Sometimes, small sinkholes recur or continue to eat soil for years without damage. At other times they middle of streetssurprising swallowing cars. Or they occur areas, swallowing houses. Sinkholes are not discriminating. They have swallowed small inexpensive homes, as well as huge homes worth millions of dollars. It is very rare for people to be hurt when sinkholesoccur, because theyusually happenover some time and arenoisy as the ground becomes unstable.
Sinkholes have also swallowed lakes. There are areas in Florida where 40 or more homes had been built around a beautiful lake. One day an entire lake disappeared because the cavern beneath the ground opened. Instead of sand being above the cavern, there was lake water, which flowed into the cavern, leaving behind dead and dying fish and plants and docks that led to nowhere. In one neighborhood, the neighbors managed to plug the hole in the lake with a huge block of concrete, and rain eventually filled the lake. But their efforts were to no avail because several years later the lake disappeared again.
Sinkholes are a natural phenomenon caused in particular geological areas by particular events. Unfortunately, even knowing the cause and having time to plan, it is not possible to stop a sinkhole.
The author indicates that the layers of material in soil from the top down are
A. surface, limestone, clay, and sand
B. surface, clay, sand, and limestone
C. surface, limestone, sand, and clay
D. surface, sand, clay, and limestone
See the picture in the passage
Đáp án D.