Insert the following items into a BST (binary search tree), in the following order: [10,5,13,3,11,1,4]. At which point in the above insertion sequence does the BST first become non-balanced (i.e., after inserting which element)? Select one: a. 10 b. 5 c. 13 d. 11 e. 4 f. 3 g. 1