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  3. Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters

Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters

admin2021-03-28  67
问题     Astronomers have had difficulty accounting for certain planets discovered outside our solar system. They are called hot Jupiters because each is similar in mass to Jupiter, the largest solar-system planet, but orbits its parent star at a fraction of the distance at which Earth, let alone Jupiter, orbits the Sun. In the standard, solar-system-based theory of planetary formation, such as a massive planet could not form so close to a star. So most attempts to explain a hot Jupiter’s existence envision it forming farther away, then migrating inward. According to one hypothesis, the planet’s gravitational field tugs on the protoplanetary disk of dust and gas from which it formed. The disk exerts its own gravitational tug, and this interplay of forces robs the planet of momentum in its orbital path, forcing it to spiral in toward the star. According to another hypothesis, the planet’s gravitational field is so strong that it creates a groove in the disk, partitioning it into inner and outer regions; the resulting gravitational interactions between the planet and these regions cause the planet to lose orbital momentum and spiral inward. Another question remains: what prevents the planet from continuing its spiral until it collides with the star?
Which of the following elements is part of one but not both of the hypotheses discussed in the passage?
选项 A、an interplay of gravitational forces
B、a loss of orbital momentum
C、a protoplanetary disk composed of dust and gas
D、a protoplanetary disk divided into two regions.
E、The movement direction of hot Jupiters
答案D
解析 这道题目相当于问两个假说之间的区别。D项是假说二特有的。A、B、C、E这四项都是共同点。
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本试题收录于： GRE VERBAL题库GRE分类
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