1 托福阅读改革后 5 篇真题集22023.8.27 How Earth's Oceans FormedAn understanding of how Earth's oceans were formed must begin with an examination of how our solar system developed. Scientists believe our solar system began forming as a huge cloud of dust that collapsed to form a sun surrounded by a flat disk of particles rotating around it, This disk-the solar nebula, as it is called-was denser in the center than it was in its outer reaches. It was also hotter in the center-perhaps as hot as 1,200 degrees Celsius, in the region where Earth now finds itself. And because the central part of the disk was hotter, it was also rockier. Only rocky grains,could survive the intense heat; ice, including water ice, would have been vaporized.1.The word "intense' in the passage is closest in meaning toA.centralB.extremeC.destructiveD.constant2.According to paragraph 1, which of the following best describes the solar nebula?A.It was a collection of dust particles replaced by a rotating sun.B.It was a disk-shaped region containing rocky grains rotating around a central sun.C.It was a disk-shaped region of water vapor made from ice vaporized by heat from a central sun.D.It was a cloud of dust grains, which collected in the hotter outer reaches of the cloud.As the dust grains were falling down into the solar disk,they began to collide and stick together, especially once they were in the disk. Clumps formed, then▉ bigger clumps, until soon the space that is now occupied by the inner planets (Mercury, Venus, Earth, and Mars) was littered with ten billion rocks the size of asteroids, about five or ten miles across. These rocks were large enough to attract one another gravitationally. As they orbited the Sun in the same direction, they forced each other into higher velocities, but whenever they collided, they slowed one another down . Scientists have calculated that the net effect of these▉ competing influences would be to keep the relative yelocities of the rocks low, and thus the collisions between them gentle 一 gentle enough that two colliding rocks would often stick together rather than fly apart. Within a million years after the▉ Sun first formed.most of the dust in the inner solar system had settled onto 30 or so planet "embryos" (planets in their early.undeveloped stage of formation) the size of Mercury.▉These embryos rotated around the Sun, but they did not stay on safe, circular orbital paths for long. The gravitational attraction among them soon forced the issue. The embryos' orbits became more elliptical (egg shaped), and their paths began to cross-and so they began to collide, not gently, but at speeds of tens of thousands of miles per hour. Only the embryos that started out somewhat larger 3than the rest could survive such impacts, and they proceeded to grow even larger by absorbing the others. Within 10 to 100 mill...
