At his death, Trevor had a probate estate consisting of $4 million of property. Which of the following is a true statement about Trevor's estate or estate tax?
A. Trevor must have an adjusted gross estate of at least $4 million.
B. Trevor must have a taxable estate of at least $4 million.
C. Trevor must have a gross estate of at least $4 million.
D. Trevor must have estate tax base (cumulative taxable transfers) of at least $4 million.