6. Depletion cost per unit is computed by dividing the total cost of a natural resource by the estimated number of units in the resource. True False 7. Natural resources include standing timber and underground deposits of oil, gas, and minerals. True False 8. The process of allocating the cost of natural resources to expense is called amortization. True False 9. In calculating depreciation, both plant asset cost and useful life are based on estimates. True False 10. A change in the estimated salvage value of a plant asset requires a restatement of prior years' depreciation True False