Which of the following examples would correspond with a principal-agent problem?

• A doctor recommending an unnecessary surgery because it generates income for her
• A company emitting pollution because it is cheaper than producing cleanly, but it is causing people in the area to get sick
• The local electric company responding slowly to an outage because they don't have to worry that customers will switch providers
• Purchasing a car then realizing it had been in previous accidents and required a lot of repairs you did not anticipate