Choose the best answer by writing the letter item (a, b, c, or d) in the blank box. In Huffman coding:

a. A collection of binary trees stores the products of character frequencies.

b. Two binary trees with minimal weights are successively combined into a single tree with the sum of their weights.

c. The codes assigned to characters are the weights of the nodes visited in a tree traversal.

d. Decoding proceeds from the leaves to the root by following the edge indicated by the previous bit of the encoding.