TPO 16 PLANETS IN OUR SOLAR SYSTEM - 英檢

想請問大家一題

第五段

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.


6. According to paragraph 5, which of the following statements is true of
both Jovian and terrestrial planets?
○The thicker the atmosphere, the smaller the planet's mass
○The more varied the gases in the atmosphere, the higher the temperature
○The higher the surface gravity, the higher the escape velocity
○The less the atmosphere contributes to the total mass, the lower the
temperature


答案是C

但是higher the escape velocity 在文中是指Jovian planets

我選B，不過A在其他段有出現而且敘述無誤..... 不知道有沒有人可以幫我解釋一下

謝謝

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