Depreciation on a particular piece of machinery was N2,700 during the fifth year of its service life and N4,050 during the sixth year. The logical explanation for this is that?

• A an addition was made to the asset during the sixth year
• B the estimate of salvage value on this equipment was decreased
• C a unit-of-output method of depreciation was used during the sixth year
• D the estimate remaining service life of the assets was increased at the beginning of the sixth year