The pre-order traversal of binary search tree is 10, 5, 1, 7,40, 50. What is the post-order traversal of the tree? a. 1, 7, 5, 50, 40, 10 b. 1, 5,7, 10, 40, 50 c. 50, 40, 10, 7,5, 1 d. 50, 40, 7. 1.5, 10