Which tree traversal visits the left subtree, then the root, then the right subtree?

• A. Pre-order visits root, then left subtree, then right subtree.
• B. In-order visits left subtree, then root, then right subtree.
• C. Post-order visits left subtree, then right subtree, then root.
• D. Level-order visits root, then its children from left to right.

Answer: (B)

This question tests in-order traversal. In-order traversal visits the left subtree, then the current node (the root), then the right subtree. The pattern described—left, root, then right—matches exactly this traversal, making it the correct choice.

This traversal is especially meaningful in binary search trees, where visiting nodes in this order yields values in sorted order, because all values in the left subtree are less than the root and all values in the right subtree are greater. The other traversals follow different orders: pre-order visits the root before its subtrees, post-order visits the subtrees before the root, and level-order goes level by level from top to bottom.