Answer: In a pure competition market, the determining factor that buyers use to select products is price. Therefore, the correct answer is option D: price.
Explanation: In a pure competition market, the determining factor that buyers use to select products is price. In a pure competition market, there are many buyers and sellers, and the products offered by the sellers are largely the same. In this type of market, buyers will typically choose the product with the lowest price, as there is little difference between the products offered by the different sellers. Other factors, such as quality, brand, and profit, may also play a role in a buyer's decision, but in a pure competition market, price is typically the most important factor.