[請益] TPO16 Planets in Our Solar System

看板TOEFL_iBT (TOEFL_iBT托福)作者Diablotin (咕嚕咕嚕)時間15年前 (2011/06/13 06:11)推噓0(0推 0噓 0→)

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Paragraph 5: The Jovian planets have very thick atmospheres consisting of varying amounts of hydrogen, helium, methane, and ammonia. By comparison, the terrestrial planets have [meager] atmospheres at best. A planet's ability to retain an atmosphere depends on its temperature and mass. Simply stated, a gas molecule can evaporate from a planet if it reaches a speed known as the escape velocity. For Earth, this velocity is 11 kilometers per second. Any material, including a rocket, must reach this speed before it can leave Earth and go into space. The Jovian planets, because of their greater masses and thus higher surface gravities, have higher escape velocities (21-60 kilometers per second) than the terrestrial planets. Consequently, it is more difficult for gases to "evaporate" from them. Also, because the molecular motion of a gas depends on temperature, at the low temperatures of the Jovian planets even the lightest gases are unlikely to acquire the speed needed to escape. On the other hand, a comparatively warm body with a small surface gravity, like Earth's moon, is unable to hold even the heaviest gas and thus lacks an atmosphere. The slightly larger terrestrial planets Earth, Venus, and Mars retain some heavy gases like carbon dioxide, but even their atmospheres make up only an infinitesimally small portion of their total mass. 5. The word [meager] in the passage is closest in meaning to ○over time ○long ago ○simply ○certainly 答案是B 不懂怎麼選的耶...... 又要請戰友們幫忙了快考試啦～好緊張 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 174.1.41.12 ※ 編輯: Diablotin 來自: 174.1.41.12 (06/13 06:12)