Which of the following is true regarding estate tax portability election? A) Allows a decedent's unused unified federal gift and estate tax exemption to be passed to his or her surviving spouse. B) Allows the estate executor to pick a decedent's state of residence for state death tax purposes. C) Allows any liability for federal estate tax to be transferred to a decedent's heirs. D) Allows the taxpayer's unified federal gift and estate tax exemption to be transferred to an ex-spouse in divorce proceedings.