The basic difference between the short run and the long run is that: select one:
a. all costs are fixed in the short run, but all costs are variable in the long run.
b. the law of diminishing returns applies in the long run, but not in the short run.
c. at least one resource is fixed in the short run, while all resources are variable in the long run.
d. economies of scale may be present in the short run, but not in the long run.