阅读理解. What exactly are white lions?'They are a color variation of regular lions,'says William Swanson,director of animal research at the Cincinnati Zoo,in Ohio. White lions are the result of a rare color gene mutation(变异)．When both a male and a female lion carry the same white genes,there is a good chance that one or more of their cubs(幼兽)will be born with white fur. Not many lions carry the white mutation.In nature,it's rare.A mutation can make an animal's survival more difficult.For example,being white makes it harder for the animal to mix with its surroundings.Mutations also can cause physical problems,so those animals generally do not survive long enough to reproduce. But sometimes white lion cubs are born among wild lions,especially in two areas of South Africa. In 1975 two white cubs were spotted in the wild in South African reserve.They were seized and sent to a zoo.Today about 500 cubs of those two white lions and a few others known to have the white color gene live around the world in zoos,circuses,farms and private preserves. White lions may be extremely rare in the wild,but breeders(饲养动物的人)know how to create more of them.This has created serious concern and debate. White lions continue to exist only because they are inbred by people-fathers and daughters,sisters and brothers.Scientists worry that it also will cause health issues for white lions. Inbreeding to create white lions as moneymaking attractions is only one concern.Another concern is that some people want to release captive－bred(人工繁殖的)white lions into the wild in South Africa to restore balance to the ecosystem.However,not everyone agrees that releasing these white lions into the wild is a good idea.Dan York of Hillsdale College has been studying white lion genetics and is worried.He says that because so many of today's white lions are inbred,it could spread health problems.If they breed with wild lions,they'll pass on the genetic problems to the wild population. Instead of releasing captive－bred white lions,York suggests that South Africa concentrate on protecting all of its wild lions.That would ensure the safety of the wild population of lions, which may produce healthy white cubs in the future. 1．It'sdifficultforawhiteliontosurvivebecause__________. a．itsfurcontrastssharplywiththesurroundings b．themutationmaycausephysicalproblems c．itislikelytobeattackedbywildlions d．itishuntedbyhumanbeings A．a,b B．a,d C．a,c D．b,d 2．What does the underlined word 'inbred' in Paragraph 7 probably mean? A．kept in enclosed space and unable to run away B．bred in human－controlled environments with restricted settings C．produced by breeding among closely related members D．born among wild lions and kept in the zoo 3．One of the reasons for inbreeding white lions is that __________. A．they can bring people a profit B．their fur can be of great use C．people want to keep white lions as pets D．people want to study the genes of white lions 4．Which of the following agrees with Dan York's opinion? A．It's useless studying white lion genetics. B．White lion cubs born among wild lions are more healthy than captive－bred ones. C．White lions shouldn't be kept in zoos or circuses. D．The ecosystem in South Africa is being seriously damaged. 5．It can be inferred from the passage that __________. A．white lions are seldom seen in the wild B．color gene mutation is common among lions C．South Africa is taking strict measures to protect its wild lions D．white lions will disappear from the earth soon