2021年5月22日托福阅读真题+题目+答案：Formation of the Solar System

2021年5月22日托福阅读真题+题目+答案：Formation of the Solar System

Where did the solar system come from? This question has tantalized astronomers for centuries. While we do not yet have a wholly complete answer, a consensus has arisen about the most likely series of events that led to the present-day system of the Sun and planets.

A key piece of evidence about the origin of the solar system is that all the planets orbit the Sun in the same direction and in nearly the same plane.As long ago as the eighteenth century, German philosopher Immanuel Kant and French scientist Pierre-Simon deLaplace independently suggested that this state of affairs could not be a coincidence.They proposed that our entire solar system-the Sun as well as all of the planets, satellites,asteroids, and comets—formed from a vast, rotating cloud of gas and dust called the solarnebula. ln the modern version of their theory, the solar nebula is thought to have had a mass somewhat greater than that of our present-day Sun.

1.The phrase “state of affairs” in the passage is closest in meaning to

O situation

O unusual combination

O type of movement

O similarity

2.According to paragraph 2, which of the following statements about the eighteenth-century theory of the origin of the solar system is true?

O It was based on similarities in the movement of planets.

O It developed out of an intense competition between Kant and Laplace.

O It proposed that the Sun had a different origin than the planets,satellites, asteroids, and comets.

O It proposed that the Sun had a different origin than the planets,satellites, asteroids, and comets.

Each part of the nebula exerted a gravitational attraction on the other parts, and these mutual gravitational pulls tended to make the nebula contract.As it contracted, the greatest concentration of matter occurred at the center of the nebula, forming a relatively dense region called the protosun, which eventually developed into the Sun.The planets formed from the much lesser amount of material in the outer regions of the solar nebula. Indeed, the mass of all the planets together is only 0.1 percent of the mass of the Sun.

When you drop a ball, the gravitational attraction of Earth makes the ball travel faster and faster as it falls; in the same way, material falling inward toward the protosun would have gained speed.As this fast-moving material ran into the protosun, the energy of the collision was converted into thermal energy, causing the temperature deep inside the solar nebula to climb. While the protosun's surface temperature stayed roughly constant, the temperature inside the protosun increased even more by means of further contraction.Eventually, after perhaps 100 million years had passed since the solar nebula first began to contract, the central temperature of the protosun reached a few million degrees, and nuclear reactions began in its interior. When this happened, the contraction stopped and a true star(the Sun) was born. Nuclear reactions in the interior of the present-day Sun are the source of all the energy that the Sun radiates into space.

3.In paragraph 4, why does the author discuss fast-moving material running into the protosun?

O To contrast it with the effect of Earth's gravity on falling balls

O To help explain the process by which the protosun increased its temperature

O To indicate how filing material was able to reach the center of the protosun

O To demonstrate that the solar nebula contracted faster than was previously thought

4.According to paragraph 4, which of the following occurred to the solar nebula approximately 100 million years after it first began to contract?

O Its gravitational a traction increased greatly.

O Increasing amounts of material fell deep inside it.

O It stopped contracting.

O Its internal temperature stopped rising.

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