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第三部分：阅读理解（共15小题，每题2分，满分30分）
阅读下列短文，从每题所给的四个选项（A、B、C和D）中，选出最佳选项。
Australian scientists are trying to give kangaroo-style stomachs to cattle and sheep in a bid
to cut the emission of greenhouse gases blamed for global warming.
Thanks to special bacteria in their stomachs, kangaroo farts contain no methane（甲烷）and scientists want to transfer that bacteria to cattle and sheep who emit large quantities of the harmful gas.
While the usual image of greenhouse gas pollution is a billowing smokestack pushing out carbon dioxide, livestock passing wind contribute a surprisingly high percentage of total emissions in some countries.
"Fourteen percent of emissions from all sources in Australia is from enteric methane from cattle and sheep," said Athol Klieve, a senior research scientist with the Queensland state government.
"And if you look at another country such as New Zealand, which has got a much higher agricultural base, they're actually up around 50 percent," he said.
Researchers say the bacteria also makes the digestive process much more efficient and could potentially save millions of dollars in feed costs for farmers.
But it will take researchers at least three years to isolate the bacteria, before they can even start to develop a way of transferring it to cattle and sheep.
Another group of scientists, meanwhile, has suggested Australians should farm fewer cattle and sheep and just eat more kangaroos.
The idea is controversial（争议）, but about 20 percent of health conscious Australians are believed to eat the national symbol already.
"It's low in fat, it's got high protein levels and it's very clean in the sense that basically it's the ultimate free range animal（散养动物）," said Peter Ampt of the University of New South Wales's institute of environmental studies.
56. According to the passage, global warming is now mainly caused by _____ .
A. methane  B. carbon dioxide  C. livestock passing wind  D. not mention in this passage
57. What does the underlined phrase “the idea”（paragraph 9）refer to?
A. Australians should give kangaroo-style stomachs to cattle and sheep.
B. The bacteria could make the digestive process much more efficient.
C. Australians should farm fewer cattle and sheep and just eat more kangaroos.
D. The bacteria could potentially save millions of dollars in feed costs for farmers.
58.  How will Australian scientists solve the problem of global warming?
A. Eating more kangaroos.  
B. Killing more cattle and sheep.
C. Letting cattle and sheep pass less wind.
D. Transferring the special bacteria in kangaroos’ stomachs to cattle and sheep.