Which of the following does not involve a correction of an error?

a. Change from recording all research and development costs as a an asset and amortizing them over 30 years to expensing them in the period of expenditure.

b. Change in the useful life of a machine because it had mistakenly been classified as a truck. The firm depreciates trucks over four years useful life and machinery over ten year useful life.

c. Charge in 20x1 net income because of an arithmetic error in recording interest expense.

d. Change in depreciation expenses because of the useful life of several assets were changed. They were wearing out faster than assumed.