In $a(n),$ traversal of a binary tree, you visit the root of a binary tree between visiting the nodes of the root's subtrees.

a$.$ preorder

b$.$ postorder

c$.$ level order

d$.$ inorder

In a binary tree, if both the left and right child of a node are null

a$.$ the node is invalid

b$.$ the node contains the key$-$value pair being searched for

c$.$ the node is a leaf

d$.$ the node is the root of the tree

An iterative version of a level order traversal for a binary tree uses a$($n$)$

a$.$ stack

b$.$ bag

c$.$ queue

d$.$ priority queue