第1个回答 2011-09-15
The earth is facing a serious problem.
第2个回答 2011-09-15
The earth is facing a big problem.
第3个回答 2011-09-15
the earth will face a serious problem
第4个回答 2011-09-15
The earth is facing a big problem
第5个回答 2011-09-15
The earth is facing big problems