 8.  HELD-TO-MATURITY FINANCIALASSETS December 31 2010 2011 NT$ NT$ (In Millions) Corporate bonds, nominal interest rate ranging from 1.20%-4.75% and 1.20%-2.98% for  2010 and 2011, respectively; effective interest rate ranging from 1.00%-2.95% and  0.83%-2.89%, respectively $  9,868 $  13,790 Bank debentures, nominal interest rate ranging from 1.60%-2.11% and 1.37%-1.60% for  2010 and 2011, respectively; effective interest rate ranging from 1.25%-2.45% and  1.25%-1.40%, respectively 504 906 10,372 14,696 Less: Current portion 1,964 1,201 $  8,408 $  13,495 Year Ended December 31 2009 2010 2011 NT$ NT$ NT$ (In Millions) Balance, beginning of year $  3,051 $  2,799 $  2,551 Provision for doubtful accounts  455 215 105 Accounts receivable written off (707) (463) (235) Impact on changes of consolidated subsidiaries ─ ─ 2 Balance, end of year $  2,799 $  2,551 $  2,423 December 31 2010 2011 NT$ NT$ (In Millions) Accrued custodial receipts of MOD service $  53 $  119 Accrued custodial receipts from other carriers  387 3 Other receivables  1,699 1,946 $  2,139 $  2,068 10.  OTHER MONETARY ASSETS - CURRENT  9.  ALLOWANCE FOR DOUBTFULACCOUNTS PART III F-26