|Question||State whether each of the following is a stock or a flow, and explain.
a. The gross domestic product.
b. National saving.
c. The value of the U.S. housing stock on January 1, 2012.
d. The amount of U.S. currency in circulation as of this morning.
e. The government budget deficit.
f. The quantity of outstanding government debt on January 1, 2012.