Given the BinarySearchTree and Node Classes Discussed in Section 17

Given the BinarySearchTree and Node classes discussed in section 17.3 (partially shown below) , select an expression to complete the recursive method smallest in the Node class. The method returns the smallest data value in the binary search tree rooted at a node. public class BinarySearchTree
{
Private Node root;
Public BinarySearchTree() {...}
Public void add(Comparable obj) {...}
Public Comparable smallest()
{
If (root == null)
Throw new NoSuchElementException() ;
Else
Return root.smallest() ;
}
Class Node
{
Public Comparable data;
Public Node left;
Public Node right;
Public Comparable smallest()
{
If (left == null)
Return data;
Else
Return _______________;
}
}
}

A) left.smallest()
B) right.smallest()
C) data.smallest()
D) Math.min(left.smallest() , right.smallest() )