Explain the fallacies in each of the following:
a. Average costs are minimized when marginal costs are at their lowest point.
b. Because fixed costs never change, average fixed cost is a constant for each level of output.
c. Average cost is rising whenever marginal cost is rising.
d. The opportunity cost of drilling for oil in Yosemite Park is zero because no firm produces anything there.
e. A firm minimizes costs when it spends the same amount on each input.