题目内容：
根据材料，回答问题。Human demands on natural resources have doubled in less than 50 years and now outstripping what the Earth can provide by more than half, a new report has warned. If this situation continues, globally it will need the capacity of two Earths by 2030, the Living Planet Report said. And the report, from the World Wide Fund For Nature, the Zoological Society of London and the Global Footprint Network, said British people are still consuming far more than the Earth can offer.
Wildlife in tropical countries is also under huge pressure, with populations of species falling by 60 percent in three decades. The study, which looked at 8,000 populations of 2,500 species and studied the change in land use and water consumption across the globe, warmed that if everyone lived such a lifestyle as they like, humans would need 2.75 planets to survive. The world's people are now living lifestyles which would require one and a half planets to support their lives, though there are significant differences between rich and poor nations.
The UK comes 31st in a list of countries based on their "ecological footprint"--the amount of land and sea each person needs to provide the food, clothes and other products they consume and to absorb the carbon dioxide they give off. The country has fallen down the league table from having the 15th biggest footprint in the last report two years ago, but the World Wide Fund For Nature points out this is due to an increase in other countries' influence not a reduction in the UK's use of resources. Ireland has the 10th highest ecological footprint in the world, while the United Arab Emirates, Qatar, Denmark, Belgium and the USA are the five worst countries for
over-consumption of resources.
It also carried a warning about the loss of wildlife and ecosystems which people depend on for food, fuel, clean water and other resources--with populations of species declining by 30 percent worldwide between 1970 and 2007.
In this text the author wants to tell us __________ . A．humans are overusing the planet
B．we need two earths to live on by 2030
C．differences between rich and poor nations
D．wildlife on earth is under huge pressure
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