Final answer:
Market conduct refers to the pricing behavior and product policy of firms within the market, not the degree of market concentration, making 'a and b only' the correct answer.
Step-by-step explanation:
The concept of market conduct includes various behaviors exhibited by firms within a market. This includes a. the pricing behavior of the firm or group of firms, such as how they set the prices for their products or services, and b. the product policy of the firm or group of firms, which involves strategies related to product design, features, quality, and the introduction of new products. The option c. the degree of seller and buyer concentration in the market is generally associated with market structure rather than conduct. Therefore, the correct answer to the question of what market conduct includes is d. a and b only, meaning it covers pricing behavior and product policy of the firm or group of firms.