The opportunity cost of money is
a) The time and trouble it takes to obtain money, such as the time it takes to goto the atm machine and make a withdrawal.
b) the risk that money can be lost or stolen.
c) the interest that could have been earned if one's wealth were held in bonds instead of money.
d) the inconvenience of switching out of bonds and into money, and vice versa.
e) all of these answers.