Answer: size and concentration of the customer base.

The correct answer is **C** because the bargaining power of buyers is primarily influenced by the size and concentration of the customer base. A smaller number of buyers increases their negotiating leverage, allowing them to demand price reductions or better terms. This contrasts with **A**, which relates to supplier power, and **B**, which pertains to the threat of substitutes. For instance, auto manufacturers, as a concentrated buyer group, can negotiate aggressively with parts suppliers, illustrating the impact of buyer power on industry dynamics.

Author: LeetQuiz Editorial Team