2015年4月12日托福阅读真题P2+题目+答案：Origin of the Solar System

2015年4月12日托福阅读真题P2+题目+答案：Origin of the Solar System

The orderly nature of our solar system leads most astronomers to conclude that the planets formed at essentially the same time and from the same primordial (original) material as the Sun. This material formed a vast cloud of dust and gases called a nebula. The nebular hypothesis suggests that all bodes of the solar system formed from an enormous nebular cloud consisting mostly of hydrogen and helium as well as a small percent of all the other heavier elements known to exist. The heavier substances in this frigid cloud of dust and gases consisted mostly of such elements as silicon, aluminum, iron, and calcium—the substances of today’s common rocky materials. Also prevalent were other familiar elements, including oxygen, carbon, and nitrogen.

15. According to paragraph 1, which of the following best describes the “nebular hypothesis”?

A Our solar system formed from a large cloud consisting mostly of hydrogen and helium and of small amounts of other elements.

B Our solar system formed from gases and heavier elements thrown off by the Sun as it rotated in the center of the nebular cloud.

C The primordial matter that evolved into our solar system consisted mostly of familiar elements such as oxygen, carbon, and nitrogen.

D A cloud of dust and gases gathered into a rotating nebula composed mostly of the rocky materials seen on Earth today.

16. The word “frigid” in the passage is closet in meaning to

A moving

B giant

C original

D cold

Nearly five billion years ago, some external influence, such as a shock wave traveling from a catastrophic explosion (supernova), may have triggered the collapse of this huge cloud of gases and minute grains of heavier elements, causing the cloud to begin to slowly contract due to the gravitational interactions among its particles. As this slowly spiraling nebula contracted, it rotated faster and faster for the same reason ice-skaters do when they draw their arms toward their bodies. Eventually, the inward pull of gravity came into balance with the outward force caused by the rotational motion of the nebula. By this time the once vast cloud had assumed a flat disk shape with a large concentration of material at its center, called the protosun (pre-Sun). Astronomers are fairly confident that the nebular cloud formed a disk because similar structures have been detected around other stars.

17. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.

A Possibly due to some explosion about five billion years ago, this nebular cloud began to collapse, causing gravitational contractions as its particles interacted.

B About five billion years ago, a supernova may have exploded, causing a huge cloud of gases and heavier elements to form

C Gravitational attraction among particles of gases and heavier elements caused some explosive event nearly five billion years ago.

D About five billion years ago, a shock wave from an external event caused this huge cloud of gases to collapse into small grains of heavier elements.

18. In paragraph 2, why does the author describe how ice-skaters use their arms to increase their speed of rotation?

A To help describe the armlike structures on a spiraling nebula

B To help explain why a nebula rotates faster when it contracts

C To show why spinning ice-skaters are not pulled down by gravity

D To show how the motion of a nebula differs from that of an ice-skater

19. The word “detected” in the passage is closet in meaning to

A formed

B predicted

C discovered

D recorded

20. According to paragraph 2, why do astronomers believe that the nebular cloud formed a disk around the protosun?

A They can still see some debris from the disk.

B They have observed that disks have formed around other stars.

C They know that any rotating cloud of gas tends to contract into a disk shape.

D They have conducted experiments with gravity that have confirmed their belief.

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