As of the Most Recent Supreme Court Ruling on the Matter

 As of the most recent Supreme Court ruling on the matter,  

A)  state governments can't tax federal bonds, but the federal government can tax state bonds. 
B)  state governments and the federal government are free to tax each other's bonds. 
C)  state governments and the federal government may not tax each other's bonds. 
D)  state governments can tax federal bonds, but the federal government can't tax state bonds. 
E)  whether a state government can tax federal bonds or the federal government can tax state bonds must be decided on a case-by-case basis.