Final answer:
Among timber, gas, gravel, oil, and land, land is the only item that is not subject to depletion because it is not a consumable resource like the others.
Step-by-step explanation:
The question asks which of the listed options is not subject to depletion. Depletion refers to the reduction in the quantity of a resource due to its consumption or extraction. Based on the information provided, the correct answer is e. Land.
Resources like timber, gas, gravel, and oil are all consumable and become depleted as we extract and use them. For example, oil and natural gas are finite resources that will eventually run out; oil deposits were formed over millions of years and cannot be replenished quickly. Similarly, timber and gravel are extracted and used at rates that may exceed their natural replenishment. However, land does not fit this description as it is not a consumable resource. Although land can be degraded or its utility altered through processes like erosion, salinization, or development, the physical presence of land itself is not depleted in the same way as the other resources.