4.C　标题归纳题。文章围绕应不应该去南极洲旅游这一话题进行讨论,C项最适合作标题。

　　B

　　Fish species are expected to shrink in size by up to 24% because of global warming,say scientists.

　　The scientists believe that global warming has a greater affect on marine ecosystems(海洋生态系统)than previously thought.Previous research has suggested that changing ocean temperatures would affect both the distribution and the reproductive abilities of many species of fish.This new work suggests that fish size would also be heavily affected.

　　The researchers built a model to see how fish would react to lower levels of oxygen in the water.They modeled the influence of rising temperatures on more than 600 species between 2001 and 2050.As ocean temperatures increase,so do the body temperatures of fish.But,according to Dr William Cheung,from the University of British Columbia,the level of oxygen in the water is the key.Warmer waters could decrease ocean oxygen levels and significantly reduce fish body weight.On the other hand,rising temperatures directly increase the metabolic rate(新陈代谢率)of the fish’s body function.This leads to an increase in oxygen demand for normal body activities.So the fish will run out of oxygen for growth at a smaller body size.

　　The research team also used its model to predict fish movements as a result of warming waters.The group believes that most fish populations will move towards the Earth’s poles at a rate of up to 36km per decade.

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