21. Consider the following binary search tree.
Starting from an empty binary search tree, the insertion of which of the following sequences of integer keys
could produce the binary tree above?
(A) 5, 9, 1, 7, 3, 4
(B) 5, 7, 4, 9, 3, 1
(C) 5, 4, 7, 3, 9, 1
(D) 5, 3, 4, 9, 1, 7
(E) 5, 3, 1, 7, 9, 4
