单选题 It is always hard for a small fish to live in a big pond. Pluto's recent departure from the classical planet family clearly proves that size really matters.
Astronomers voted on August 24 to give a definition to the word "planet", and Pluto turned out to be only a "dwarf planet" (矮行星). After weeks of heated debate, over 2,500 astronomers from 73 countries voted on the definition of a "planet" at a conference of the International Astronomical Union (IAU). According to the definition, a planet must have a clear neighborhood around its orbit. Pluto has widely been considered a planet since its discovery in 1930. Unfortunately, it has a special orbit which overlaps with Neptune's. It is all because, compared with Neptune, Pluto is very small. It is attracted by Neptune's gravity when the two planets get closer.
According to IAU, a "dwarf planet" should have an orbit around the sun, It will not have a clear neighborhood around its orbit, and must not be a satellite. The new classification means that the science textbooks will have to be updated. The solar system is now made up of the eight "classical planets", together with a number of dwarf planets. The classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Astronomers sent an advanced telescope into space, and found a belt of objects, which lies beyond Neptune. The belt contains nearly 1,000 objects, including Pluto. As they continued the exploration, scientists recently discovered at least 41 dwarf planets at the edges of the solar system. There are at least two objects of a similar size to Pluto.
It seems that even if the IAU had kept Pluto's status as a planet, the classical theory of nine planets in the solar system would have had to be changed. More dwarf planets of a similar size to Pluto would join the family of planets. Scientists will probably find many more dwarf planets.

单选题 The sentence "It is always hard for a small fish to live in a big pond" quoted at the beginning of the passage is used to ______.

A. tell us small fish can hardly survive in the big pond
B. tell us the size of an object really matters
C. mean that small planet can hardly exist in the solar system
D. explain the disappearance of Pluto in the solar system

【正确答案】 B

【答案解析】[解析] 文中第一段第二句提到，冥王星脱离行星家族证明了天体的体积的重要性。

单选题 According to the passage, Pluto is ______.

A. a "dwarf planet" which has a clear neighborhood around its orbit
B. a satellite of Neptune which was discovered in 1930
C. the smallest planet in the solar system
D. a "dwarf planet" which has an orbit around the sun

【正确答案】 D

【答案解析】[解析] 从文中第二段第一句话得知，冥王星属于矮行星。另外，根据第三段第一句话得知矮行星有一个围绕太阳的轨道。

单选题 According to the new classification, the solar system includes ______.

A. eight classical planets and forty one dwarf planets
B. nine classical planets and at least forty one dwarf planets
C. eight classical planets and a number of dwarf planets
D. 1,000 objects

【正确答案】 C

【答案解析】[解析] 参见第三段第四句话。

单选题 From the last paragraph we can infer that if IAU kept Pluto's status as a planet, the number of planets in the solar system would he ______.

A. eight
B. nine
C. less than nine
D. more than nine

【正确答案】 D

【答案解析】[解析] 从最后一段话得知，即使将冥王星归为行星，对于太阳系包括九大行星之说也需要修改，因为更多的矮行星也将被归为行星，所以太阳系中的行星数量会大于九个。

单选题 Which of the following statements is NOT true according to the passage?

A. According to the definition of a "planet", if Pluto were bigger it would not have left the classical planet family.
B. The definition of "planet" was determined by over 2,500 astronomers.
C. Pluto has a special orbit which overlaps with Neptune's because it is so small as to be attracted by Neptune's gravity when the two planets get closer.
D. A "dwarf planet", which must not be a satellite without a clear neighborhood around its orbit, should have an orbit around the Sun.

【正确答案】 A

【答案解析】[解析] 此题可以用排除法。选项B可以由第二段第二句话证明正确。选项C可以由第二段最后两句话证明正确，选项D可以由第三段一、二句话证明正确。