Classify each of the following as to whether it is an example of a positive question or a normative question (some may have elements of both).
a. "What is the level of the U.S. national debt?
b. "Is the national debt too high?"
c. "How low should the unemployment rate be?"
d. "What policies can lower the unemployment rate?"
e. "What kinds of production should be counted in measuring gross domestic product?"
f. "Is it better to have low unemployment or low inflation?"