Pursuant to Corey's Will, Emma (Corey's Sister) Inherits His Property

Pursuant to Corey's will, Emma (Corey's sister) inherits his property. Emma dies in a later tax year. The estate tax attributable to the inclusion of the property in Corey's gross estate was $300,000. The estate tax attributable to the inclusion of the property in Emma's gross estate is $400,000. Emma's credit for the tax on prior transfers is:

A) $0 if Emma died nine and one-half years after Corey.
B) $300,000 if Emma died three years after Corey.
C) $400,000 if Emma died one year after Corey.
D) $180,000 if Emma died five and one-half years after Corey.