下列选项中，哪个可能是下图的广度优先遍历序列（ ）。
图为有向图，共 999 个结点（1∼91 \sim 91∼9），有向边如下：
1 → 3, 1 → 5 2 → 1 3 → 2, 3 → 4, 3 → 7 4 → 2 5 → 3 6 → 8 7 → 5, 7 → 6 8 → 9 9 → 4, 9 → 7
1,3,5,7,4,2,6,8,91, 3, 5, 7, 4, 2, 6, 8, 91,3,5,7,4,2,6,8,9
9,4,2,1,3,7,5,6,89, 4, 2, 1, 3, 7, 5, 6, 89,4,2,1,3,7,5,6,8
1,3,5,7,6,8,9,4,21, 3, 5, 7, 6, 8, 9, 4, 21,3,5,7,6,8,9,4,2
9,4,7,2,1,3,5,6,89, 4, 7, 2, 1, 3, 5, 6, 89,4,7,2,1,3,5,6,8