价         量      账面价值

年初          10      1,000    10,000

年中            8       (500)     (5,000) (4000cash received, 500*10=5000 will be written off from BV, Realized gain/loss=-                                                       2*500=or=4000-5000=    - 1000)

年底                     500      5,000 YE BV           

                    2        500      1,000 YE FV 年底 市价    量    

                                        (4,000) YE MTM G/L

凑合着看吧。高手不答我就捡个机会捞点钱。