Final answer:
The legal advertisement Owner A can post is 'Room for Rent: Cozy bedroom in a safe neighborhood, perfect for students,' which complies with fair housing guidelines by not discriminating on protected classes.
Step-by-step explanation:
Owner A wants to rent a room in her house, and it's important that her advertisements comply with fair housing guidelines to ensure they are legal.
Of the options presented, the advertisement stating "Room for Rent: Cozy bedroom in a safe neighborhood, perfect for students" would be considered legal as it does not discriminate on the basis of sex, family status, or race/ethnicity which are protected classes under the Fair Housing Act.
On the other hand, specifying that only female tenants are allowed, excluding children, or discriminating based on ethnicity or religion are all practices that are not in line with fair housing laws and consequently would be considered illegal.