The ___ node is the only mode that has no parent

A. Root

B. Binary

C. child

D. n-ary

A. Root

Explanation:

A root node is a node which has no parent. All other nodes have a parent and zero or more children. Root node is the only node for which parent is null.

As an example consider the following tree structure:

Node R has 2 children C1, C2. C1 in turn has 2 children C11, C12. C2 again has two children C21 and C22. As we can see, each node C1, C2, C11, C12, C21, C22 has well defined parents with the only exception of the root R.