Extracted text: The post-order of a binary search tree is 5, 18, 15, 20, 10, 35, 45, 50, 40, 30 then the pre-order is а. 30, 10, 5, 20, 15, 18, 40, 35, 50, 45 b. 30, 10, 5, 15, 20, 18, 15, 40, 35, 50, 45 с. 30, 10, 20, 5, 18, 15, 35, 50, 40, 45 d. 30, 10, 5, 20, 15, 18, 35, 40, 50, 45