Correct Answer (Detailed Explanation is Below)

B. 11, 12, 10, 16,19,18,20,15

Detailed Explanation

Explanation:

Preorder traversal (Root → Left → Right) is given:
15, 10, 12, 11, 20, 18, 16, 19

Step 1: Root

First element of preorder = 15 → Root

Split into BST parts:

• Left subtree (<15): 10, 12, 11

• Right subtree (>15): 20, 18, 16, 19

Left Subtree

Preorder: 10, 12, 11

Root = 10

• Left of 10 → none

• Right of 10 → 12, 11

Node 12:

• Left → 11

Tree:

 10
 \
 12
 /
 11

Postorder (Left → Right → Root):

11, 12, 10

Right Subtree

Preorder: 20, 18, 16, 19

Root = 20

Left subtree: 18, 16, 19

Node 18

• Left → 16

• Right → 19

Tree:

 20
 /
 18
 / \
 16 19

Postorder:

16, 19, 18, 20

Final Postorder

Left subtree + Right subtree + Root

11, 12, 10, 16, 19, 18, 20, 15