2020年9月12日托福阅读真题+题目+答案：Accounting for the High Density of Planet Mercury

2020年9月12日托福阅读真题+题目+答案：Accounting for the High Density of Planet Mercury

Venus, Earth, and Mars are all thought to have formed from similar materials. Their iron cores take up similar fractions of the planets, and their silicate mantles- -the mantle is the layer of material between a planet's central core and its outer crust- -melt to produce similar kinds of volcanic rocks. By contrast, Mercury, the smallest and closest to the Sun of the four inner, or terrestrial, planets, may have been formed from a different bulk composition, or it may have formed under different conditions than the other terrestrial planets. The planet has a huge iron core, indicating either that the planet contains at least twice the iron content of the other terrestrial planets or that virtually all the iron from the bulk composition was pulled into its core, leaving its mantle almost iron-free. At the same time, the planet shows no recent volcanic activity, and so, unlike Venus, Earth, and Mars, its interior can be assumed to be stationary. The lack of volcanic activity is usually taken to mean that the planet has largely finished losing its internal heat. Mercury, however, has a small magnetic field. Magnetic fields are generally accepted to be caused by fluid movements in the mantle caused by heat loss. Somehow Mercury has created a balance that allows the generation of a magnetic field in the absence of mantle movements.

1.The word “generation”in the passage is closest in meaning to

O production

O possibility

O operation

O presence

2.Paragraph 1 supports which of the following inferences about Venus,Earth,and Mars?

O Their mantles are almost iron-free.

O Their magnetic fields are increasing over time.

O Their mantles are fluid, and they continue to lose heat.

O They formed under widely varying conditions.

3.Paragraph 1 suggests that scientists tend to assume which of the following about planets’ internal heat?

O Its intensity depends on the planets' distance from the Sun.

O It is produced by the planets’ magnetic fields.

O It is produced by the pulling of iron toward planetary cores.

O Its loss results from volcanic activity.

4.According to paragraph 1, which of the following is unexpected give the lack of recent volcanic activity on Mercury?

O Mercury has largely finished losing its internal heat.

O Mercury's mantle is almost iron-free.

O Mercury has a magnetic field.

O There is no movement in Mercury's silicate mantle.

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