Final answer:
It is true that labor costs have generally decreased while material costs have increased in the history of power source relationships due to improvements in labor efficiency and the finite nature of resources.
Step-by-step explanation:
In the history of power source relationships, it's true that labor costs have tended to decrease while material costs have increased. This pattern is observable due to technological advancements that improve labor efficiency, and the finite nature of resources which can lead to scarcity and higher prices. In particular, resources such as oil, steel, metals, agricultural products, and heavy machinery, which are essential for energy and economic growth, continue to command high prices, as they are fundamental to powering economies and hence, are closely coupled with economic scale and energy use.