Final answer:
Among the listed plant assets, land does not depreciate over time, unlike buildings, equipment, and land improvements. The value of physical capital, including plant and equipment, generally increases over time, enhancing productivity. The correct option is C.
Step-by-step explanation:
The question seeks to identify which plant asset does not decline in service potential over its useful life. Contrary to buildings, equipment, and land improvements, which all typically depreciate over time, land itself does not usually depreciate.
The value of the physical capital, which includes plant and equipment, generally rises over time due to upgrades in the machinery or improvements made to the existing assets, contributing to increased worker productivity and output.