下面哪一个可能是下图的深度优先遍历序列? A. 1, 5, 6, 3, 2, 8, 9, 4, 7B. 1, 5, 8, 9, 7, 4, 6, 3, 2C. 3, 2, 1, 4, 7, 6, 9, 5, 8D. 2, 5, 6, 3, 8, 7, 9, 4, 1 正确答案:B