What does the following recursive method do, if called from another public method, where the parameter p is reference to the tree root? private int undefined_Method(Node p) { if (p == null) return 0; if (p.left == null || p.right == null) return p.data; if (p.left != null && p.right = null) return p.data + undefined_Method(p.left) + undefined Method(p.right); else return undefined_Method(p.left) + undefined Method(p.right); } A It returns the summation of data of the leaf nodes and nodes having only right child. B It returns the summation of data of leaf nodes and nodes having two child nodes It returns the summation of data of the leaf nodes and nodes having only left child. D It returns the summation of the data of all the nodes