{{B}}Change{{/B}} As relentlessly bad as the news about global warming seems to be, with ice at the poles melting faster than scientists had predicted and world temperatures rising higher than expected, there was at least a reservoir of hope stored here in Canada’s vast forests. The country’s 1.2 million square miles of trees have been called the "lungs of the planet" by ecologists because they account for more than 7 percent of Earth’s total forest lands. They could always be depended upon to suck in vast quantities of carbon dioxide, naturally cleansing the world of much of the harmful heat-trapping gas. But not anymore. In an alarming yet little-noticed series of recent studies, scientists have concluded that Canada’s precious forests, stressed from damage caused by global war A. are greatly damaged by global warming B. approach the threatening line C. take in less carbon dioxide than they produce D. become net carbon sources 更多"{{B}}Change{{/B}} As relentless"的相关试题: [单项选择]
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