In which of the following isolated cases should Frank, as executor of his father's estate, waive his executor's fee? a. Frank is the sole beneficiary of his father's estate. b. The estate will not incur any Federal Estate Tax. Frank is in the 35% Federal Income Tax Bracket. For Fiduciary Income Tax purposes, the estate is in the 15% tax bracket. c. Frank expects he will need to devote 50 hrs a week to the settlement of his father's estate for the next 2 years to sell his father's business. d. Frank's father hasn't filed federal income tax returns for the past 5 years.