Perched among the highlands of western Cameroon, bordered by green mountains and cliff faces, Lake Nyos is a scene of breathtaking beauty. But the picture cannot be (36) .A detailed study reveals that the lake could release a (37) cloud of car bon dioxide, capable of wiping out entire communities around its shores. The warning, from a team of scientists, comes nearly 20 years after the lake (38) an estimated 80m cubic metres of CO2 into the atmosphere. Heavier than air, the cloud of gas rolled down, (39) hillsides and villages. Silent and invisible, it (40) the air of oxygen, killing hundreds of cattle and claiming the lives of more than 1,700 people up to 26km away. "It was one of the most mysterious (41) scientists have ever investigated" said George Kling, an ecologist at the University of Michigan. Researchers called in after the 1986 (42) discovered that the lake, which sits atop a volcano, contained record levels of carbon dioxide. Gas bubbling up from the Earth’s magma was under such (43) at the bottom of the 200-metres deep lake that it dissolved until it reached max. (44) . To prevent a recurrence, in 2001 engineers installed a pipe to suck CO2 from the bottom of the lake and release it harmlessly into the air. (45) . Dr Kling’s team recommends the urgent installation of a further four pipes in each lake at a rate of one a year. (46) .
患者,男性50岁,3个月前发生上消化道出血,经检查,证实为食管静脉曲张,二天前再次出现呕血、黑便,来院急诊,过去有乙肝病史20余年,此病人诊断为门脉高压。 上消化道出血,其原因最可能为
A. 肝外门静脉阻塞
B. 肝静脉阻塞
C. 肝窦内阻塞
D. 脐静脉阻塞
E. 门静脉主干血栓形成
Passage OneQuestions 26 to 28 are based on the passage you have just heard.
A. government buildings.
B. boats and lakes.
C. theatres and shopping.
D. parks and trees.