Which of the following statements most accurately describes the estate tax concept of portability

A: It automatically applies to the surviving spouse when the first spouse dies

B: The surviving spouse is able to use her/his full exemption, plus the amount of the exemption not used by her/his deceased spouse

C: If the surviving spouse remarries, she/he may use all of the unused exemption from all prior spouses.

D: The portability provision replaced the unlimited marital deduction