英语专业八级考前全真模拟试卷[4]_专业八级

part Ⅱ proofreading & error correction ［15 min.］
proofread the given passage on answer sheet two as instructed.
part Ⅲ reading comprehension ［40 min.］
section a reading comprehension ［30 min.］
in this section there are six reading passages followed by a total of fifteen multiple-choice questions.read the passages and then mark your answers on your coloured answer sheet.
text a
black holes
the theory of stellar evolution predicts that when the core of a star has used up its nuclear fuel,the core will collapse.if the star is about the size of the sun,it will turn into a degenerate dwarf star.if it is somewhat larger,it may undergo a supernova explosion that leaves behind a neutron star.but if the stellar core has a mass greater than about three solar masses,gravitational forces overwhelm nuclear forces and the core collapses.since nuclear forces are the strongest repulsive forces known,nothing can stop the continued collapse of the star.a black hole in space is formed.
because of the intense gravitational forces near the black hole,nothing can escape from it,not even light.if we were to send a probe toward an isolated black hole,the probe would detect no radiation from the black hole.it would,however,sense a gravitational field like the one that would be produced by a normal star of the same mass.as the probe approached the black hole,the gravitational forces would increase inexorably.at a distance of a few thousand kilometers,the gravitational forces would literally be torn away from the side furthest away from the black hole.eventually,at a distance of a few kilometers from the black hole,the particles that made up the probe would pass the point of no return,and the particles would be lost forever down the black hole.this point of no return is called the gravitational radius of the black hole.
but how can we hope to observe such an object?nature,herself,could conceivably provide us with a “probe” of a black hole:a binary star system in which one of the stars has become a black hole and is absorbing the mass of its companion star.as the matter of the companion star fell into the black hole,it would accelerate.this increased energy of motion would be changed into heat energy.near the gravitational radius the matter would move at speeds close to the speed of light,and temperatures would range from tens of millions of degrees to perhaps as much as a billion degrees.at these temperatures,x and gamma radiation are produced.further,since the matter near the gravitational radius would be orbiting the black hole about once every millisecond,the x radiation should show erratic,short-term variability unlike the regular or periodic varability associated with neutron stars and degenerate dwarfs.
the x -ray source cygnus x-1 fulfills these “experimental” conditions.it is part of a binary star system in which a blue supergiant star is orbiting an invisible companion star.this invisible companion has a mass greater than about nine times the mass of the sun,and it is a strong x-ray source that shows rapid variations in the intensity of its x-ray flux.most astronomers believe that cygnus x-1 is a black hole but this belief is tempered with a dose of caution.the idea of a black hole is still difficult to swallow,but theorists can think of no other object that could explain the phenomenon of cygnus x-1.for this reason,in most scientific papers,cygnus x-1 is referred to simply as a black hole “candidate.”
16.according to the passage,a black hole would.
a.be observable through a powerful telescopeb.be invisible even at close range
c.be formed from a degenerate dwarf stard.be most likely to develop in a binary star system
17.the author regards the existence of black holes as ____.
a.experimentally confirmed b.a logical contradiction
c.theoretically possible d.in principle unprovable
text b
view of citizenship
the liberal view of democratic citizenship that developed in the 17th and 18th centuries was fundamentally different from that of the classical greeks.the pursuit of private interest with as little interference as possible from government was seen as the road to human happiness and progress rather than the public obligations and involvement in the collective community that were emphasized by the greeks.freedom was to be realized by limiting the scope of governmental activity and political obligation and not through immersion in the collective life of the polis.the basic role of the citizen was to select governmental leaders and keep the powers and scope of public authority in check.on the liberal view,the rights of citizens against the state were the focus of special emphasis.