13．Does the Yangtze River still have baiji（白鰭豚），the graceful，grey dolphin with tiny eyes and a long narrow beak？
Since November 6，a team of scientists from China，Switzerland，the United Kingdom，the United States，Germany and Japan had been searching for any sign of the freshwater dolphin in the middle and lower sections of the river．After six weeks，they came back empty-handed．Wang Ding，head of the team，said he had seen a sharp drop in the baiji population over the past few decades．However，he was still unwilling to call the species extinct and added，"We will try every effort to save them as long as they are not found to be extinct．"
As one of the world's oldest dolphin species，the baiji is shy and nearly blind．It dates back about 20 million years and is found only in the Yangtze River．It's listed as one of the 12 most endangered animal species in the world．
Around 400 baiji were believed to be living in the Yangtze until the 1 980s．In 1997，a survey spotted 13．Two years later their number was down to zero．
The rapi d disappearance of this dolphin over the past two decades coincided（巧合） with the rapid expansion of economic development along the river．Resea rchers on some dead baiji collected in recent years showed that more than 90 percent of the deaths were caused by human activities．
One reason is that over-fishing has cut the dolphin's food sources．Dams built along the river and neighbouring waterways have also kept them from swimming into and out of their habitats．Meanwhile，waste discharge（排放） has seriously polluted the river．And heavy river traffic has greatly reduced their living space．
The disappearance of the baiji would be the first case of a large aquatic（水生的） mammal being driven to extinction since hunting killed off the monk seal around 1952．
42．This passage mainly tells usA．
A．the fact that Baiji is in danger and the reason why its number reduces
B．people are trying efforts to save Baij i as long as they find them
C．human activities have caused 90 percent of Baiji's deaths
D．how serious the pollution is long the Yangtze River
43．It is known from the passage thatB．
A．scientists from foreign countries have searched for Baiji for 6 years
B．Baiji is a large aquatic mammal which is in danger of extinction
C．Baiji becomes endangered all because of human's activities
D．there are 12 endangered species altogether in the world
44．We can infer from the passage thatA．
A．riverside constructions have affected the living environment of animals
B．Baiji is one of the world's oldest species and lives longer than humans
C．it is the waste discharge that has poisoned Baiji in Yangtze River
D．nowadays scientists are no longer able to save Baiji at all
45．This passage is most probably taken fromD．
A．a(chǎn) student's diary B．a(chǎn) tour guidebook
C．a(chǎn) Biology textbook D．a(chǎn) science magazine．
分析 本文主要講述了目前長江的白鰭豚處境危險、數(shù)量減少及其原因．
解答 42-45．ABAD
42題答案：A 考查文章大意，縱觀全文可知，文章主要講的是白鰭豚處境危險的事實及其數(shù)量減少的原因，故本題答案為A選項．
43題答案：B 考細節(jié)推理，根據(jù)最后一段的The disappearance of the baiji would be the first case of a large aquatic（水生的） mammal being driven to extinction （白鰭豚的消失有可能是第一個大型水生哺乳動物被逼滅絕的案例）可知本題答案為B選項"白鰭豚是一種面臨滅絕的大型水生哺乳動物"．
44題答案：A 考查細節(jié)推理，根據(jù)倒數(shù)第二段的Dams built along the river and neighbouring waterways have also kept them from swimming into and out of their habitats．（沿河的大壩建設(shè)以及鄰近的水路也阻止了它們出入棲息地）可知本題答案為A選項"河邊的建設(shè)影響了動物的居住環(huán)境"．
45答案：D 考查文章來源 本文是一篇有關(guān)海豚是否還存在于長江的科學類研究文章，故應(yīng)該取自于"科學雜志"，因此本題答案為D選項．
點評 本文是一篇科普類閱讀，題目涉及多道細節(jié)理解題，做題時結(jié)合原文和題目有針對性找出相關(guān)語句進行仔細分析，結(jié)合選項選出正確答案．推理判斷也是要在抓住關(guān)鍵句子的基礎(chǔ)上合理的分析才能得出正確的答案．
