D, a U.S citizen who made no inter vivos gifts, died in the current year, leaving a gross estate of $5 million.

A) Will Ds executor be required to file a federal estate tax return?

B) Under what change of circumstances would a gross estate of this size require a return?

C) Since the tax liability of Ds estate is less than the Section 2010 credit, may the estate get a refund of excess credit?