In each case the depth-first sequence of an ordered rooted spanning tree for a graphG is given. Also given are the non-tree edges of G. Which of these spanning trees is adepth-first spanning tree?

• A. 123242151 and {4, 5}, {1, 3}
• B. 123242151 and {3, 4}, {1, 4}
• C. 123245421 and {3, 4}, {1, 4}
• D. 123245421 and {2, 5}, {1, 4}