A：中国
B：俄罗斯
C：加拿大
D：巴西
设m．＞n＞0，a＞0，比较am+a﹣m与an+a﹣n的大小．
根据短文，选择正确答案。
Van and Ted are twin brothers. They look the same. They are English. They are eleven. They are in No.15 Middle School. They are new students in Class One, Grade One. Van sits in Row One. Ted sits in Row Three.
