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  3. Half of the world’ s coral reefs(珊瑚礁) have died in the last 30 years. Now scientists are racing to ensure that the rest survive.

Half of the world’ s coral reefs(珊瑚礁) have died in the last 30 years. Now scientists are racing to ensure that the rest survive.

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问题    Half of the world’ s coral reefs(珊瑚礁) have died in the last 30 years. Now scientists are racing to ensure that the rest survive. Even if global warning were to stop right now, scientists predict that more than 90% of corals will die by 2050. If no major steps are taken to address the problem, the reefs may be headed for total extinction(灭绝).
   The planet’ s health depends on the survival of coral reefs. They are often described as " the rainforests of the sea" , because they provide shelter for a wide variety of sea life. In addition, the reefs serve as barriers that protect coastlines from the full force of powerful storms.
Corals are used in medical research for cures to diseases. They are key to local economies as well, since the reefs attract tourists, the fishing industry, and other businesses, bringing in billions of dollars.
   Corals are particularly sensitive to changes in temperature. A rise of just 1 to 2 degrees can force the corals to drive out the algae (水藻). Then the corals turn white in a process called "bleaching". Corals can recover from short-term bleaching, but long-term bleaching can cause permanent damage. In 1998, when sea surface temperatures were the highest in recorded history, coral reefs around the world suffered the most severe bleaching. It is estimated that even under the best of conditions, many of these coral reefs will need decades to recover.
   Although reefs face other threats from pollution, industrial activities, and overfishing, it is global climate change that most concerns scientists. Scientists remain hopeful that it’ s not too late to save the reefs, and some are moving ahead on experiments to accomplish that goal.
According to the passage,______is the biggest threat to coral reefs.
选项 A、pollution
B、overfishing
C、industrial activities
D、climate change
答案D
解析 根据第五段第一句“Although reefs face other threats from pollution，industrial activities， and overfishing， it is global climalte change that most concerns scientists．”可知，尽管珊瑚礁面临着环境污染、工业活动以及过度捕捞等威胁，但是全球气候变化依然是科学家们最为担忧的。由此可推知，气候变化是对珊瑚礁最大的威胁。故选D。
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