Which of the following represents the post-order traversal of the tree below?

A.

2, 3, 4, 7, 8, 10, 13, 15, 18

B.

2, 4, 8, 7, 3, 15, 18, 13, 10

C.

10, 3, 2, 7, 4, 8, 13, 18, 15

D.

10, 3, 13, 2, 7, 18, 4, 8, 15