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In the past 50 years, the amount of water in the open ocean with zero oxygen has increased more than four times. In coastal water bodies, including the river mouth and seas, low-oxygen sites have increased more than 10 times since 1950. Scientists expect oxygen to continue dropping even outside these zones as the Earth warms. To stop the decline, the world needs to control in both climate change and nutrient pollution.

Oxygen is a must to life in the oceans. The drop in ocean oxygen is among the most serious effects of human activities on the Earth’s environment.

This is the first time for the scientists to take such a deep look at the causes, consequences and solutions to low oxygen worldwide, in both the open ocean and in coastal waters. About half of the oxygen on Earth comes from the ocean. However, combined effects of nutrient loading and climate change are greatly increasing the number and size of “dead zones” in the open ocean and coastal waters, where oxygen is too low to support most sea life.

In areas traditionally called “dead zones”, like those in Chesapeake Bay and the Gulf of Mexico, oxygen drops to levels so low that many animals have trouble in breathing and die. As fish run away from these zones, their living areas become smaller and smaller. But the problem goes far beyond “dead zones”. Even smaller oxygen drops can hold up the growth in animals, reproduction and lead to disease or even death. Low oxygen also can cause the release of dangerous chemicals. While some animals can thrive in dead zones, overall biodiversity falls.

1.What does the underlined word “decline” mean in Chinese?

A 上升.

B 下降.

C 持平.

D 翻倍.

解析：选B。词义猜测题。根据前面的Scientists expect oxygen to continue dropping even outside these zones as Earth warms可知decline应该是drop的意思，即“下降”，故选B。

2.How much oxygen on the Earth comes from the ocean?

A 10%.

B 25%.

C 40%.

D 50%.

解析：选D。细节理解题。根据第三段第二句About half of the oxygen on Earth comes from the ocean. 可知地球上大约有一半的氧气来自海洋，故选D。

3.Why are these waters called “dead zones”?

A The oxygen in these areas is too low for the animals to live.

B Ships are easy to break down and sink in these areas.

C There are no animals living in these areas.

D Many people died in these areas.

解析：选A。细节理解题。根据第三段最后一句 However, combined effects of nutrient loading and climate change are greatly increasing the number and size of “dead zones” in the open ocean and coastal waters, where oxygen is too low to support most sea life.可知死亡区域就是指那些含氧量低到很多海洋生物无法生存的水体区域,故选A。

4.Which of the following statements is TRUE?

A All animals living in the sea need oxygen.

B Climate change will help cut down the dead zone.

C Fish grow faster and better in low oxygen area.

D Human activities have many bad effects on environment.

解析：选D。推理判断题。根据第二段第二句The drop in ocean oxygen is among the most serious effects of human activities on the Earth’s environment.可知海水含氧量下降是人类活动对地球环境造成不利影响最重要的一项，由此可推断人类活动对地球环境有很多不利影响，故选D。

5.What is the main idea of this passage?

A Dead zone in water is becoming larger.

B Oxygen in water is necessary for sea animals.

C The drop in ocean oxygen causes bad effects.

D Low oxygen can cause the release of dangerous gas.

解析：选C。主旨大意题。根据文章高频词低氧区域在扩大、低氧区域会造成海洋生物的死亡、会引起有害气体的释放、导致海洋生物多样性下降等可知本文主要讲的是海洋含氧量的下降带来的不利影响，故选C。