2021年1月9日托福阅读真题+题目+答案：The Beginning of Planet Formation

2021年1月9日托福阅读真题+题目+答案：The Beginning of Planet Formation

The four innermost planets of our solar system – Mercury, Venus, Earth, and Mars – are terrestrial, or rocky, planets. █ The beginning of their creation process occurred when the cloud of leftover material from the formation of the Sun settled into a disc around the young star. █ Most of the material in the cloud, like the material of the Sun itself, was in the form of hydrogen and helium. █ But there was a trace of dust, no more than 2 percent of the original material, in the form of particles as fine as the particles in smoke. █ Heat from the young Sun blew much of the gas away, but the rotation of the original cloud ensured that the dust settled into a disc around the young Sun – a protoplanetary disc like the ones seen around young stars today.

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

A) gathering

B) spreading

C) remaining

D) floating

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

A) showed

B) suggested

C) confirmed

D) guaranteed

3. According to paragraph 1, the cloud of material from the formation of the Sun consisted of TWO of the following. To receive credit, you must select TWO answers.

A) A very large amount of hydrogen and helium

B) Material blown from other young stars

C) Small particles of dust

D) Particles that are also found in smoke

Within the disc, all the particles were moving in the same direction around the Sun, like runners going round a track. This meant that when they bumped into one another, they did so relatively gently, not in head-on collisions, giving the particles a chance to stick to one another. The tendency to stick may have been helped by electric forces produced by particles rubbing against one another, in the same way that you can make a child’s balloon stick to the ceiling after rubbing it on a woolen sweater. Another important factor was turbulence in the gas, creating swirling structures like whirlwinds which gathered pieces of material together and gave them a chance to interact. Computer simulations show how objects as big as Ceres can form in this way – provided the particles can stick together.

4. Why does the author mention “runners going round a track,” “a child’s balloon,” and “whirlwinds” in the discussion of the interaction of particles in the Sun’s protoplanetary disc?

A) To argue that interactions among the particles were no different from certain phenomena observed on Earth

B) To help explain how different types of particle interactions were actually very similar to one another

C) To suggest that the interactions among the particles were simpler than astronomers once believed

D) To use relatively familiar concepts to illustrate particle interactions that contributed to planet formation

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