2019年5月26日托福阅读真题+题目+答案：Chemical and Biological Weathering of Rocks

2019年5月26日托福阅读真题+题目+答案：Chemical and Biological Weathering of Rocks

Rocks can be broken into smaller pieces by a natural process known as weathering. Weathering refers to the chemical alteration and physical disintegration of rocks by the actions of air, water, and organisms. Two principal types of weathering are chemical weathering and biological weathering.

The minerals that rocks are made of are subject to alteration by chemical weathering. Some minerals, such as quartz, resist this alteration quite successfully, but others, such as the calcium carbonate of limestone, dissolve easily. In any rock made up of a combination of minerals, the chemical breakdown of one set of mineral grains leads to the disintegration of the whole mass. In granite (made chiefly of the minerals quartz and feldspar), the quartz resists chemical decay much more effectively than does the feldspar, which is chemically more reactive and weathers to become clay. Often granite surfaces are heavily pitted (marked with many small holes or depressions). In such cases, the feldspar grains are likely to have been weathered to clay and blown or washed away. The quartz grains still remain, but they may eventually be loosened too. So even a rock as hard as granite cannot withstand the weathering process forever.

。。。。。余下真题省略！

1. What is the author’s purpose in discussing quartz and limestone?

A) To explain why quartz is more common than limestone

B) To point out that most rocks are made up of a combination of minerals

C) To illustrate that some minerals are more affected by chemical weathering than others are

D) To show that chemical weathering can occur only in the calcium-carbonate form of a mineral

2. The word “withstand” in the passage is closest in meaning to

A) continue

B) avoid

C) experience

D) resist

3. According to paragraph 2, why does granite often have a pitted appearance?

A) Granite does not contain enough feldspar to prevent chemical weathering.

B) The quartz grains in granite decay when they chemically react with feldspar.

C) The feldspar grains weather away from the granite surface.

D) The clay in the granite has been blown or washed away, leaving behind the quartz and feldspar.

。。。。。余下真题题目省略！

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