托福阅读常考话题及练习题推荐四：地下水（2）

1托福阅读常考话题：地下水练习题

Paragraph 1: Most of the world’s potable water----freshwater suitable for drinking----is accounted for by groundwater, which is stored in the pores and fractures in rocks. There is more than 50 times as much freshwater stored underground than in all the freshwater rivers and lakes at the surface. Nearly 50 percent of all groundwater is stored in the upper 1,000 meters of Earth. At greater depths within Earth, the pressure of the overlying rock causes pores and cracks to close, reducing the space that pore water can occupy, and almost complete closure occurs at a depth of about 10 kilometers. The greatest water storage, therefore, lies near the surface.

1.In paragraph 1, why does the author mention “the pressure of the overlying rock”?

A. To show how water can be forced deep under Earth’s surface

B. To show why groundwater is more plentiful than surface freshwater

C. To correct a commonly made error about the location of groundwater

D. To explain why most groundwater lies near Earth’s surface

2.According to paragraph 1, groundwater differs from the water in rivers and lakes in terms of its

A. portability

B. usefulness

C. abundance

D. cost

Paragraph 2: Groundwater is stored in a variety of rock types. A groundwater reservoir from which water can be extracted is called an aquifer. We can effectively think of an aquifer as a deposit of water. Extraction of water depends on two properties of the aquifer: porosity and permeability. Between sediment grains are spaces that can be filled with water. This pore space is known as porosity and is expressed as a percentage of the total rock volume. Porosity is important for water-storage capacity, but for water to flow through rocks, the pore spaces must be connected. The ability of water, or other fluids, to flow through the interconnected pore spaces in rocks is termed permeability. In the intergranular spaces of rocks, however, fluid must flow around and between grains in a tortuous path; this winding path causes a resistance to flow. The rate at which the flowing water overcomes this resistance is related to the permeability of rock.

3.The word “extracted” in the passage is closest in meaning to

A. used

B. poured

C. removed

D. kept out

4.The word “termed” in the passage is closest in meaning to

A. considered

B. called

C. limited to

D. caused by

5.According to paragraph 2, what does porosity determine?

A. The rate at which the aquifer’s water overcomes resistance to flow

B. The amount of water that the aquifer can hold

C. The likelihood that fractures and joints will occur in the aquifer

D. The depth underground at which the aquifer lies

6.According to paragraph 2, what is the relationship between permeability and porosity?

A. The more pores a rock has, the higher its porosity but the lower its permeability.

B. Rocks with many internal spaces that are not connected with each other will have high porosity but low permeability.

C. If water flows through a rock easily, it has high permeability but low porosity.

D. Rocks that have high permeability have high porosity and vice versa.

Paragraph 3: Sediment sorting and compaction influence permeability and porosity. The more poorly sorted or the more tightly compacted a sediment is, the lower its porosity and permeability. Sedimentary rocks----the most common rock type near the surface----are also the most common reservoirs for water because they contain the most space that can be filled with water. Sandstones generally make good aquifers, while finer-grained mudstones are typically impermeable. Impermeable rocks are referred to as aquicludes. Igneous and metamorphic rocks are more compact, commonly crystalline, and rarely contain spaces between grains. However, even igneous and metamorphic rocks may act as groundwater reservoirs if extensive fracturing occurs in such rocks and if the fracture system is interconnected.

7.The word “compacted” in the passage is closest in meaning to

A. hard

B. compressed

C. heavy

D. deeply buried

8.According to paragraph 3, when can igneous rock serve as an aquifer?

A. When it has many connected fractures

B. When it lies next to metamorphic rock

C. When it lies relatively near the surface

D. When it is crystalline

Paragraph 4: The water table is the underground boundary below which all the cracks and pores are filled with water. In some cases, the water table reaches Earth’s surface, where it is expressed as rivers, lakes and marshes. Typically, though, the water table may be tens or hundreds of meters below the surface. The water table is not flat but usually follows the contours of the topography. Above the water table is the vadose zone, through which rainwater percolates. Water in the vadose zone drains down to the water table, leaving behind a thin coating of water on mineral grains. The vadose zone supplies plant roots near the surface with water.

9.The word “coating” in the passage is closest in meaning to

A. stream

B. barrier

C. amount

D. layer

10.Paragraph 4 implies which of the following about the roots of plants?

A. They prevent water from reaching the vadose zone.

B. They mark the boundary between the vadose zone and the water table

C. They do not typically get their water from the water table.

D. They help keep the water table from dropping farther.