Final answer:
Using freshwater for irrigation is the most likely cause of freshwater depletion over time.
Step-by-step explanation:
The most likely cause of freshwater depletion over time would be using freshwater for irrigation. Irrigation refers to the process of supplying water to crops for their growth. This process consumes a significant amount of freshwater, which, if not managed sustainably, can lead to the depletion of freshwater resources.
For example, in regions where agriculture heavily relies on irrigation, such as parts of California's Central Valley, excessive water usage for irrigation has resulted in the depletion of aquifers and groundwater reserves.
Therefore, among the given options, option OD, using freshwater for irrigation, would most likely cause the depletion of a freshwater resource over time.
Learn more about freshwater depletion