第1个回答 2011-12-21
The causes of global warming are large volumes of greenhouse gas has been discharged and large areas of forest (have) been cut down.
第2个回答 2011-12-21
The causes of global warming are that a great number of greenhouse gas have been discharged and large areas of forest cut down本回答被提问者采纳
第3个回答 2011-12-21
Climate warming that greenhouse gas emissions are by emissions, large area of forests have been cut down