At Her Death Serena Owned Real Estate Worth $210,000 with Her

At her death Serena owned real estate worth $210,000 with her spouse in joint tenancy with the right of survivorship. Serena contributed $50,000 to the original cost of the property and her spouse contributed the remaining $100,000. What amount, if any, is included in Serena's gross estate?

A) $80,000.
B) $50,000.
C) $105,000.
D) zero - this property qualifies for the marital deduction.
E) None of the choices are correct.