A
In the past 50 years, the amount of water in the open ocean with zero oxygen has gone up more than fourfold. In coastal water bodies，including river mouths and seas, lowoxygen sites have increased more than tenfold since 1950.Scientists expect oxygen to continue dropping even outside these zones as Earth warms.
“Oxygen is fundamental to life in the oceans，” said Denise Breitburg, a marine ecologist with the Smithsonian Environmental Research Centre. “The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth's environment. Actually, it's a great loss to all the support services that rely on recreation and tourism, including hotels and restaurants and taxi drivers and everything else. The reverberations(严重影响) of unhealthy ecosystems in the ocean can be extensive.”
In areas traditionally called “dead zones”， like those in Chesapeake Bay and the Gulf of Mexico, oxygen plummets(大幅下跌) to so low levels that many animals die. As fish avoid these zones, their habitats become smaller and they're easier to be attacked or caught. But the problem goes far beyond “dead zones”. Even smaller oxygen decline can prevent growth in animals, hinder reproduction and lead to disease or even death. It can also cause the release of dangerous chemicals such as nitrous oxide, a greenhouse gas up to 300 times more powerful than carbon dioxide. While some animals can boom in “dead zones”， overall biodiversity falls.
Climate change is the key criminal in the open ocean. Warming surface waters make it harder for oxygen to reach the inside of the ocean. Furthermore, as the ocean as a whole gets warmer, it holds less oxygen. In coastal waters, too much nutrient pollution from land creates algal blooms, which use up oxygen as they die and break down.
People's livelihoods are also on the line, the scientists reported, especially in developing nations. Smaller fisheries(渔场) may be unable to relocate when low oxygen destroys their harvests or forces fish to move elsewhere. So we humans have to carry on a war now and win the war.
语篇解读：本文是一篇说明文。人类活动导致全球变暖，气候变化使海洋中的氧气含量下降影响海洋生物的生存，这些相应地会影响人类的生存，人类必须采取措施应对此问题。
1．What does the first paragraph mainly talk about?
A．The ocean has been losing its oxygen.
B．The amount of sea water is increasing.
C．The coastal water bodies are dangerous.
D．Earth becomes warmer and warmer.
解析：选A 段落大意题。通读第一段可知海洋面临的现状，在过去的50年里，海洋中零氧水域的水量增加了四倍多，低氧场所自1950年以来增加了十倍多。通过这些现状科学家预计，随着地球变暖，即使在这些区域之外，氧气含量也会继续下降，故选A。
2．What can we infer from Denise Breitburg's words?
A．Different oceans have different levels of oxygen.
B．The decline in ocean oxygen has great influences.
C．The future of tourism relies on the levels of ocean oxygen.
D．The decrease in ocean oxygen is the most serious environmental problem.
解析：选B 推理判断题。根据第二段Denise Breitburg所说的话可知，海洋氧气的减少是人类活动对地球环境最严重的影响之一，这种不良的海洋生态系统的严重影响还会扩大，由此可见海洋氧气的减少有很大影响，故选B。
3．How does the “dead zone” affect sea animals?
A．It offers more food.
B．It forms dangerous gas.
C．It reduces their living areas.
D．It produces more carbon dioxide.
解析：选C 推理判断题。根据第三段中的In areas traditionally called “dead zones” ... oxygen plummets(大幅下跌) to so low levels that many animals die.As fish avoid these zones, their habitats become smaller and they're easier to be attacked or caught.可知，在“死亡地带”，氧气大幅下跌，许多动物死去。当鱼类避开这些区域时，它们的栖息地变小，更容易被攻击或捕获，故选C。
4．How can we win the war according to the text?
A．By closing smaller fisheries.
B．By controlling humans' bad activities.
C．By improving people's living standards.
D．By stopping nutrients entering the ocean.
解析：选B 推理判断题。根据第二段中的The decline in ocean oxygen ranks among the most serious effects of human activities on the Earth's environment.Actually, it's a great loss to all the support services that rely on recreation and tourism, including hotels and restaurants and taxi drivers and everything else.可知，是人类活动导致了海洋氧气减少，所以要解决此问题必须控制人类的有害活动，故选B。
