Classical economists traditionally believed that:
a. a change in the money supply can affect real gdp.
b. there are three motives for demanding money.
c. the transactions demand for money influences the velocity of money.
d. the economy does not always operate at full employment.
e. the velocity of money is constant.

In terms of the "great wheel of science", statistics are central to the research process (a) only between the hypothesis phase and the observation phase (b) only between the observation phase and the empirical generalization phase (c) only between the theory phase and the hypothesis phase (d) only between the empirical generalization phase and the theory phase