Final answer:
Rental listings can have discriminatory requirements in California that are considered illegal in other states.
Step-by-step explanation:
In California, it is legal and ethical to have rental listings that include specific eligibility criteria, such as 'No smokers' or 'No pets.' However, these types of listing requirements are considered discriminatory and thus illegal in some other states. It is important to note that the Fair Housing Act prohibits discrimination based on specific protected classes, such as race, color, religion, sex, national origin, familial status, and disability.
For example, if a rental listing in California specifies that only applicants without children are allowed, it would be considered legal, but in many other states, it would be illegal due to its discriminatory nature.
So, the correct answer is 1) Rental listings.