Australian scientists are trying to give kangaroo-style stomachs to cattle and sheep in order to cut the greenhouse gases they send out, which is thought to be responsible for global warming.    Thanks to special bacteria in their stomachs, kangaroo flatulence contains nomethane  and scientists want to transfer that bacteria to cattle and sheep who produce large quantities of the harmful gas.    While the usual image of greenhouse gas pollution is a billowing smokestack pushing out carbon dioxide, farm animals' passing wind contributes 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 make 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. And about 20 percent of health-conscious Australians have eaten 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 free-range animal," said Peter Ampt of the University of New South Wales's institute of environmental studies. The passage is written mainly to   _  .
discuss a better way to protect the earth warn farmers of the danger of animal waste illustrate the possible solutions to pollution present a recent study on one cause of global warming
Question: Australian scientists are trying to give kangaroo-style stomachs to cattle and sheep in order to cut the greenhouse gases they send out, which is thought to be responsible for global warming.    Thanks to special bacteria in their stomachs, kangaroo flatulence contains nomethane  and scientists want to transfer that bacteria to cattle and sheep who produce large quantities of the harmful gas.    While the usual image of greenhouse gas pollution is a billowing smokestack pushing out carbon dioxide, farm animals' passing wind contributes 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 make 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. And about 20 percent of health-conscious Australians have eaten 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 free-range animal," said Peter Ampt of the University of New South Wales's institute of environmental studies. The passage is written mainly to   _  .
A. discuss a better way to protect the earth
B. warn farmers of the danger of animal waste
C. illustrate the possible solutions to pollution
D. present a recent study on one cause of global warming
Answer: