单选题 A company using straight-line depreciation has an ending gross investment in fixed assets of $ 750, an accumulated depreciation of $ 300, and an annual depreciation expense of $150. The average depreciable life of the fixed assets and the average age of the plant and equipment are : Depreciable life Avg age of P&E ①A. 2 years 5 years ②B. 5 years 2 years ③C. 7 years 5 years