问题详情：
The world’s astronomers came to their senses yesterday and approved a new definition of the word “planet” that would drop tiny Pluto from the club and relegate it instead to a lesser realm of “dwarf planets.” It was a welcome step away from a proposal that would have kept Pluto as a planet but meantime opened the door for dozens of small, icy bodies on the fringes of the solar system.
The important vote came after fierce debate at a meeting of the International Astronomical Union, which had been considering a proposal to define a planet as any object that orbits a star and is large enough for its own gravity to pull it into a spherical (球形的) shape. That definition was scientifically precise but led to results that offended common sense. An asteroid, a small moon, and another icy ball like Pluto would suddenly have risen to planet-hood, swelling the number of planets to 12, with many more icy rocks likely to qualify as more was learned about them.
Fortunately, the astronomers have now added another requirement to the definition. Planets must not only be large enough to be round, they must also have cleared out the neighborhood around their orbits. Pluto would not qualify — it orbits in a belt of icy debris on the edge of the solar system. Neither would an icy rock nicknamed Xena, which orbits in that same zone, nor Ceres, a big asteroid that marches in the company of other asteroids. Pluto’s moon, Charon, which had qualified under the first proposal, is also out of the running.
Pluto, with its small size and oddball orbit, should never have been deemed a planet in the first place. Henceforth there will be eight planets, at least three dwarf planets, and tens of thousands of “smaller solar system bodies,” like comets and asteroids. Our only regret is that the astronomers chose the name “dwarf planets” for Pluto’s new category instead of abandoning the word entirely when discussing these less-than-planetary bodies.
46. We can know from the passage that the new definition of planet __________.
A. has been welcomed by all walks of life
B. will kick the Pluto out of the planet group in the solar system
C. still makes the Pluto as a planet
D. will enlarge the number of planets in our solar system into permanently 12
47. After the new definition of “planet” was put forward, all of the following are regarded as planet except________.
A. Venus B. Ceres C. Mars D. Jupiter
48. The writer’s attitudes towards the new definition of “planet” is________.
A. welcome B. indifferent C. hostile D. neutral
49 If the original definition of “planet” had not been changed, there would be the following consequences except that ________.
A. thousands of icy rocks in space will be classified as planets
B. some asteroids big enough to pull itself into a spherical shape will be regarded as planets.
C. the Pluto will be relegated to “dwarf planet”
D. there will be at least twelve or even more planets in the solar system.
50. We can infer from the article that the decision to apply new definition to “planet”________.
A. has won universal support from scientists.
B. has been severely criticized by many astronomers
C. has not been made inconsiderately.
D. has been banned by the International Astronomical Union
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