Final answer:
A higher price encourages a firm to increase its output by purchasing more materials and hiring more workers, because it aims to maximize profits which is reflected in a positively sloped supply curve. So the correct option is D.
Step-by-step explanation:
The individual supply curve is positively sloped primarily because a higher price for goods and services motivates a firm to increase its output. This is due to the fact that, with higher prices, the firm stands to make more profit. Answering the question, the correct statement is D: A higher price encourages a firm to increase its output by purchasing more materials and hiring more workers.
Essentially, if a firm can sell its products at a higher price, the potential for increased profits exists. To capitalize on this opportunity, the firm may invest in more materials and labor to produce more goods. It believes that by doing so, it will be able to maximize its profits before prices potentially drop again. This assumption can be seen in the behavior of the supply curve; when costs of production fall or when firms can sell their output at higher prices, they supply a larger quantity, resulting in the curve shifting to the right.
By contrast, if the costs of production rise, the firm's potential profit decreases, usually resulting in the firm supplying a smaller quantity of the product, which can be observed as a leftward shift of the supply curve.