Final answer:
The answer that is not a source of economies of scale is D) inelastic resource supply curves. While learning-by-doing, labor specialization, and the use of larger machines support economies of scale, inelastic resource supply curves can lead to higher costs as production increases.
Step-by-step explanation:
The question asks which of the following is not a source of economies of scale: A) learning-by-doing, B) labor specialization, C) use of larger machines, D) inelastic resource supply curves. Economies of scale occur when the quantity of output goes up, resulting in the cost per unit going down. This can happen through various means, such as process improvements, increased efficiency, or volume discounts in purchasing. Learning-by-doing, labor specialization, and the use of larger machines are all classic sources of economies of scale. They contribute to increased efficiency and reduced average costs. In contrast, inelastic resource supply curves do not lead to economies of scale. If an input is inelastic, this means that its availability does not significantly change with price, which can result in increased costs as production scale increases if the input is a significant cost driver.
Therefore, the correct answer is D) inelastic resource supply curves, which are not a source of economies of scale.