People who take a "layer cake" view of federalism believe that

a.) state governments are too weak to meet most citizen needs.
b.) state governments are supreme over the national government.
c.) national and state governments must cooperate to meet citizen needs.
d.) national and state governments are exclusively sovereign in their areas.

The correct answer is D.) national and state governments are exclusively sovereign in their areas. Basically, the layers of the cake are separate in what they do, but together they make a good cake. In politics terms, this is called the layer cake system or the dual federalism system. They are sovereign in their own things but they also work together.