Final answer:
The true statement about learning curves is that there are significant differences in how quickly different organizations learn. This variance is due to a myriad of influences within each organization, such as the adoption of new technologies, structural and cultural differences.
Step-by-step explanation:
The question pertains to the concept of learning curves, which refer to the relationship between experience and efficiency in production. Specifically, the question asks which statement is true about learning curves. The correct answer is a), which asserts that there are substantial differences in the rates at which organizations learn. This is due to various factors, such as organizational structure, culture, and the implementation of new technologies. On the other hand, b) is incorrect because the learning rate is indeed influenced by numerous organizational factors; c) is not accurate because the learning curve is more about production efficiency increases with experience rather than a function of numbers of units sold; and d) is misleading because while total cost per unit can be a measure of performance, the learning curve itself represents a broader concept beyond just the cost per unit.