An economy's production possibilities frontier: select one:
a. is based on the assumption that technology is constantly changing.
b. demonstrates that, although resources are scarce for individuals, there is no problem of scarcity for society as a whole.
c. is based on simplifying assumptions, but is still useful for illustrating scarcity, opportunity cost, and economic growth.
d. explain the immense complexity of the real economy.
e. is based on unrealistic assumptions and therefore has no value as an economic tool.

Richardson hired j. c. flood company, a plumbing contractor, to correct a stoppage in the sewer line of her house. the plumbing company's 'snake' device, used to clear the line leading to the main sewer, became caught in the underground line. to release it, the company excavated a portion of the sewer line in richardson's backyard. in the process, the company discovered numerous leaks in a rusty, defective water pipe that ran parallel with the sewer line. to meet public regulations, the water pipe, of a type no longer approved for such service, had to be replaced either then or later, when the yard would have to be excavated again. the plumbing company proceeded to repair the water pipe. though richardson inspected the company's work daily and did not express any objection to the extra work involved in replacing the water pipe, she refused to pay any part of the total bill after the company completed the entire operation. j. c. flood company then sued richardson for the costs of labor and material it had furnished. (c) for what, if anything, should richardson be liable? explain."