2014英语专业八级全真模拟试题(3)

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When the end of the world comes, we'll know what to blame. Scientists have found compelling evidence thatthe Sun has a baby brother, a dark star whose eccentric orbit is responsible for periodically showering the Earthwith comets and meteorites.

The dark star--named Nemesis by astronomers--is thought to be a brown dwarf that spins round the Sun inan orbit so large that it is measured in light years, the distance light travels in a year, equivalent to about 6,000billion miles.

The research suggests that, every 26m years, the star's eccentric orbit brings it within one light year of the solarsystem. There it causes havoc in the Oort Cloud, a huge region surrounding the solar system that contains billionsof bits of cosmic rubble left over from the formation of planets.

Of the millions of rocks it throws out of orbit at each visit, some hurtle earthwards--and have several times nearly wiped out life on Earth.
Astronomers have long wondered if the Sun has a smaller partner. Recently, two independent groups of researchers have found evidence of one.

One group, led by John Matese, professor of physics at the University of Louisianaat Lafayette, confirms thenotion that it is most likely to be a brown dwarf, a star that never accumulated enough mass to ignite and which hassimply sat in space smoldering for billions of years.

Matese studied 82 comets from the Oort Cloud and found common elements in the shape of their orbits thatcould only be explained if they had been influenced by the gravitational pull of an object severn1 times the size ofJupiter and existing about 25,000 times farther from the Sun than the Earth.

Matese said: "A companion to the Sun orbiting at these distances would have little effect on the planets. But itwould play a big role in the way comets 'made their way, from their birth places in the planetary disc out to the: Oort Cloud and in how they can return to the inner solar system."
Further research was published by Richard Muller, professor of physics at the University of California,
Berkeley, following analyses of moon rock samples brought back to Earth by Apollo 14.
The absence of a protective atmosphere means the moon has been subjected to intense bombardment in its 4.5 billion-year existence.
Muller's breakthrough was to find a way to date how long ago any particle was melted---meaning he could build up a picture of whether the moon gets a constant barrage or suffers spells of intensebombardment.

He said: "The evidence clearly shows that the moon has gone through spells of relatively fiequent impacts andothers of reduced intensity. I believe it is likely that this is because the Oort Cloud is being disturbed by a massivebody that is throwing comets out of stable orbits, a small fraction of which could reach the Earth."
Muller and others believe that the dark star probably takes about 26m years to complete an orbit around the stm.
Other scientists have already noted that mass extinctions of life on Earth seem to occur in a pattem with gaps equivalent to multiples of 26m, suggesting some regular event is causing the comets to come Earth's way.

The best-known such event was the one that wiped out the dinosaurs 65m years ago, but that was not the worst; the planet has suffered several such large mass extinctions.
Astronomers have found the first Earth-sized planet orbiting another star. The discovery raises the chances of finding planets that could support life as we know it.

21. Which of the following is NOT a feature of the Nemesis?
A. It contributes to showering of comets on the earth.
B. It is a smaller partner of the Sun.
C. It has a large orbit.
D. It contains bits of cosmic rubble.

22. What does the passage imply about a brown dwarf?.
A. It's bright.
B. It's not very big.
C. It's not a planet.
D. It's huge.

23. The Nemesis influences the comets by__
A. exerting effects on their birthplace
B. gravitational pull of planets
C. affecting the Oort Cloud
D. influencing their way to the Oort Cloud and the inner solar system

24. Muller found that ___
A. the star orbits around the sun
B. the star is disturbed by the Oort Cloud
C. the star is influencing the Oort Cloud
D. the star is responsible for extinction of life on the Earth

25. A suitable title for the passage could be __.
A. Brown Dwarf Orbits around the Earth
C. Oort Cloud and Comet ShowerB. Sun "s Hidden Twin Stalks Earth
D. Star, Planet and Dwarf

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