Reading Comprehension
试题详情
文章：
| Line | Io and Europa, the inner two of Jupiter’s four |
| largest moons, are about the size of Earth’s moon | |
| and are composed mostly or entirely of rock and | |
| metal. Ganymede and Callisto are larger and roughly | |
| (5) | half ice. Thus, these four moons are somewhat |
| analogous to the planets of the solar system, in which | |
| the rock- and metal-rich inner planets are distinct | |
| from the much larger gas- and ice-rich outer planets. | |
| Jupiter’s moons are, however, more “systematic”: | |
| (10) | many of their properties vary continuously with |
| distance from Jupiter. For example, Io is ice-free, | |
| Europa has a surface shell of ice, and while | |
| Ganymede and Callisto are both ice-rich, outermost | |
| Callisto has more. | |
| (15) | This compositional gradient has geological |
| parallels. Io is extremely geologically active, Europa | |
| seems to be active on a more modest scale, and | |
| Ganymede has undergone bouts of activity in its | |
| geological past. Only Callisto reveals no geological | |
| (20) | activity. In similar fashion, Callisto’s surface is very |
| heavily cratered from the impact of comets and | |
| asteroids; Ganymede, like Earth’s moon, is heavily | |
| cratered in parts; Europa is very lightly cratered; and | |
| no craters have been detected on Io, even though | |
| (25) | Jupiter’s gravity attracts comets and asteroids |
| passing near it, substantially increasing the | |
| bombardment rate of the inner moons compared | |
| to that of the outer ones. But because of Io’s high | |
| degree of geological activity, its surface undergoes | |
| (30) | more-or-less continuous volcanic resurfacing. |
题目：
The author’s reference to Jupiter’s gravity in line 25 serves primarily to
选项:
A、indicate why the absence of craters on Io’s surface is surprising
B、explain the presence of craters on the surface of Jupiter’s four largest moons
C、provide an explanation for the lack of geological activity on Callisto
D、contrast Jupiter’s characteristics with the characteristics of its four largest moons
E、illustrate the similarity between Jupiter’s four largest moons and the planets of the solar system
答案:
A
