The preorder traversal sequence of a binary search tree is 30, 20, 10, 15, 25, 23, 39, 35, 42. Which one of the following is the post order traversal sequence of the same tree?
(A) 10,20,15,23,25,35, 42,39,30
(B) 15,10,25,23,20, 42,35,39,30
(C) 15,20,10,23,25, 42,35,39,30
(D) 15,10,23,25,20,35, 42,39,30