Banks Are Important to the Study of Money and the Economy

Banks are important to the study of money and the economy because they

A) provide a channel for linking those who want to save with those who want to invest.
B) have been a source of financial innovation that is expanding the alternatives available to those wanting to invest their money.
C) are the only financial institution to play a role in determining the quantity of money in the economy.
D) do all of the above.
E) do only A and B of the above.