A. together
Supply and demand work together to determine the price of goods and services in a market. When demand for a product increases (and supply remains the same), the price tends to rise. Conversely, if demand decreases (with supply remaining the same), prices typically fall. Similarly, if supply increases (and demand remains steady), prices usually drop, while decreased supply tends to increase prices. In a competitive market, prices naturally adjust as the interaction between supply and demand responds to changes in consumer preferences, available resources, and market conditions.
While there is competition in markets, the interaction between supply and demand is not competitive but rather a cooperative process that balances price levels.
While other factors like government regulations or external events may influence prices, supply and demand are the primary factors that determine price.
Supply and demand do not work separately; they are interdependent and work together to determine prices in the market.
Therefore, A. together is the correct answer.