To Whom Does the Spousal Exemption for Federal Estate Tax

To whom does the spousal exemption for federal estate tax apply?

A) To spouses of decedents
B) To spouses of decedents unless it is a same-sex marriage in a state that does not permit same-sex marriages
C) To the blocked inheritances of the spouse of a living or deceased child
D) To those whose estates are below $1,000,000