小马过河,小马过河官网,出国留学,雅思培训,托福培训,SAT培训,GRE培训,GMAT培训,小语种培训,出国留学一站式服务,小马过河国际教育官方网站 > 托福 > 托福机经 > 文章正文

2018年1月28日托福考试阅读机经预测

时间:2018-01-21 11:33 来源:未知 作者:小马过河 阅读量 (
栏目摘要: 2018年1月28日托福考试阅读机经预测之真题测练 真题来源:2015-4-12CN 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...

2018年1月28日托福考试阅读机经预测之真题测练

  真题来源:2015-4-12CN 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.

48.jpg

  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.

  During the collapse, gravitational energy was converted to thermal energy (heat), causing the temperature of the inner portion of the nebula to dramatically rise. At such high temperatures, the dust grains broke up into molecules and energized atomic particles. However, at distances beyond the orbit of Mars, the temperatures probably remained quite low. At -200°C, the tiny particles in the outer portion of the nebula were likely covered with a thick layer of ices made of frozen water, carbon dioxide, ammonia, and methane. Some of this material still resides in the outermost reaches of the solar system in a region called the Oort cloud.

  The formation of the Sun marked the end of the period of contraction and thus the end of gravitational heating. Temperatures in the region where the inner planets now reside began to decline. The decrease in temperature caused those substances with high melting points to condense into tiny particles that began to coalesce (join together). Such materials as iron and nickel and the elements of which the rock-forming minerals are composed—silicon, calcium, sodium, and so forth—formed metallic and rocky clumps that orbited the Sun. Repeated collisions caused these masses to coalesce into larger asteroid-size bodies, called protoplanets, which in a few tens of millions of years accumulated into the four inner planets we call Mercury, Venus, Earth, and Mars. Not all of these clumps of matter were incorporated into the protoplanets. Rocky and metallic pieces that still remain in orbit are called meteoroids.

  As more and more material was swept up by the inner planets, the high- velocity impact of nebular debris caused the temperatures of these bodies to rise. Because of their relatively high temperatures and weak gravitational fields, the inner planets were unable to accumulate much of the lighter components of the nebular cloud. The lightest of these, hydrogen and helium, were eventually whisked from the inner solar system by the solar winds.

  At the same time that the inner planets were forming, the larger, outer planets (Jupiter, Saturn, Uranus, and Neptune), along with their extensive satellite systems, were also developing. Because of low temperatures far from the Sun, the material from which these planets formed contained a high percentage of ices—water, carbon dioxide, ammonia, and methane—as well as rocky and metallic debris. The accumulation of ices partly accounts for the large sizes and low densities of the outer planets.

  The two most massive planets, Jupiter and Saturn, had surface gravities sufficient to attract and hold large quantities of even the lightest elements—hydrogen and helium.

  2018年1月27日托福考试阅读机经预测之高频词汇(部分内容):

词汇同义词释义
a case in pointa good example一个恰当的例子
a wealth of dataa lot of information数据库
abruptsudden突然的
acceleratespeed up加速
accessiblereachable易接近的
accordinglycorrespondingly因此
account forexplain解释
accustomed toused to习惯于,适应
acutesevere严峻的
addressdealt with处理
adequaterich      充足的,富有的
adhesivesticky粘合剂
adjacent tonext to邻近的
admiration forhigh opinion of赞赏
adoptuse采用
advantageousprofitable有利的
adventarrival到达
adverseunfavorable不利的
advocatesupport主张,拥护
aggregateaccumulate聚合
aim to dointend to do想要做…
akin tosimilar to与…相似
allegedlysupposedly据说,假设

  以上是2018年1月28日托福考试阅读机经预测内容,获取托福考试真题,让你熟悉和熟练掌握托福考试题目。本次机经真题较多,希望考生可以早做准备,从而预留出更多的时间来备考。


获取免费学习资料

托福相关

MORE

友情链接