It is always hard for a small fish to live in a big pond. Pluto's recent departure from th

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 create the first scientific definition of the word planet, and Pluto obviously didn't make the cut. It 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. The debate over Pluto's status started in 1992. After an advanced telescope was sent into space, astronomers started find 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, but the other way around. More dwarf, planets of a similar size to Pluto would join the family of planets. Scientists will probably find many more dwarf planets.
【小题1】According to the passage, Pluto is .A．a planet which has a clear neighborhood around its orbitB．a satellite of Neptune which was discovered in 1930C．the smallest planet in the solar systemD．a planet which has an orbit around the sun【小题2】The sentence It is always hard for a small fish to live in a big pond quoted in the beginning of the passage is used to .A．tell us a small fish can hardly survive in the big pondB．tell us the size of an object really mattersC．mean that a small planet can hardly exist in the solar systemD．explain the disappearanee of Pluto in the solar system【小题3】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 be .A．eightB．nineC．less than nineD．more than nine【小题4】Which of the following statements is NOT true aceording to the passage?A．According to definition of a planet, if Pluto were bigger it would not have left the classic planet family.B．It's quite possible for dwarfs to lose if they compete with big menC．Pluto has a special orbit which overlap with Neptune's, because it is so small as to be attraeted by Neptune's gravity when the two planets get closerD．A dwarf planet, which can not be a satellite without a clear neighborhood around its orbit, should have an orbit around the Sun.D

(答案→)D 解析：文章讲述了冥王星被排除出太阳系9大行星的范围。【小题1】细节题。根据第三段第一行According to IAU, a dwarf planet should have an orbit around the Sun。【小题2】推理题。文章通过冥王星被排除出太阳的行星家庭告诉我们大小很重要。冥王星正是因为太小了，而被排除在外。【小题3】推理题。根据文章最后一段可知在太阳系里有另外好几个星星和冥王星差不多大，如果不把冥王星排除，那么就要有另外几个星星进入行星家庭，太阳的行星就会超过9个。【小题4】细节题。根据文章第一段可知A正确。根据第二段最后一句可知C正确。根据第三段1,2行可知D正确。B的意思和文章的内容不搭。

就是这个解释

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