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Australia’s Great Barrier Reef will lose most of its coral cover by 2050 and, at worst, the world’s largest coral system could collapse by 2100 because of global warming, a study recently said.
The study by Queensland University’s Center for Marine Studies, commissioned (委托) by the Worldwide Fund for Nature, said that the destruction of coral on the Great Barrier Reef was unavoidable due to global warming, regardless of what actions were taken now. “Under the worst-case scenario, coral populations will collapse by 2100 and the reestablishment of coral reefs will be highly unlikely over the following 200-500 years,” said the report entitled “Implications (可能的影响) of Climate Change for Australia’s Great Barrier Reef.”
The Great Barrier Reef is the world’s largest living reef formation stretching 2,000 km north to south along Australia’s northeast coast. “Only if global average temperature change is kept to below two degrees Celsius can the Reef have any change of recovering from the predicted damage,” the report said. Coral has a narrow comfort zone and is highly stressed by a temperature rise of less than one degree Celsius. Water temperature rises of less than one degree coincided (同时发生) with the world’s worst recorded coral bleaching (颜色变淡) period in 1988. The warmer water forces out the algae (海藻) that give coral its color and, if all are lost, the coral dies and the reef will die out. In 1988, 16 percent of the world’s coral died, with 46 percent of the Indian Ocean coral destroyed.
Scientists express water temperatures to rise this century by between two and six degrees Celsius. “There is little to no evidence that corals can adapt fast enough to match even the lower  temperature rise,” said the report. Over-fishing and pollution from coastal farms were also contributing to the destruction of coral on the Great Barrier Reef.
The Great Barrier Reef supports huge fishing and tourism industries. Even under favorable conditions tourists would only be able to experience real corals in reef “theme parks”.
49. The underlined word “scenario” in Paragraph 2 probably means         .
A. imagination        B. intention        C. expectation       D. prediction
50. From the passage, we can infer that         .
A. corals have no difficulty in adapting the temperature change
B. if we take quick actions we can avoid the destruction of corals
C. we can find corals in many areas of the seas or oceans
D. the algae help corals to live
51. Which of the following is NOT the cause of the destruction of coral on the Great Barrier Reef?
A. Direct sunshine.              B. Over-fishing.
C. Global warming.              D. Pollution.
52. By saying “Coral has a narrow comfort zone” (Para. 3), the author means         .
A. coral can only live in a small area     
B. coral prefers a crowded place
C. coral can hardly adapt to the temperature change     
D. coral grows best in a small area