Key Points
A binary tree is a tree data structure in which each node has at most two child nodes.
The number of subtrees of a node is called the degree of the node. In a binary tree, all nodes have degrees o, 1, and 2.
The degree of a tree is the maximum degree of a node in the tree. A binary tree is of degree 2. The number of nodes of degree 2 in Tis "n-1".

Hence the correct answer is n-1.
