The correct sequence of constructing Huffman tree is A. Repeat until root…

Correct sequence: Create leaf nodes, Build priority queue, Combine lowest-frequency nodes, Repeat until root formed.

1. Create leaf nodes: Make a leaf node for each symbol with its frequency.

2. Build the priority queue: Insert all leaf nodes into a min-priority queue (min-heap) keyed by frequency.

3. Combine the two lowest-frequency nodes: Remove the two nodes with smallest frequencies, create a new internal node whose frequency is their sum, and insert the new node back into the priority queue.

4. Repeat until a single root remains: Continue removing and combining the two smallest nodes until only one node (the root of the Huffman tree) remains.

Why this order matters: You must first have leaf nodes to populate the priority queue. The queue provides the two lowest-frequency nodes at each step; combining them creates larger nodes that are reinserted, and repeating this process produces the final Huffman tree.