Answer: D. offering to advertise a property, for a fee, for a "For Sale by Owner" seller
It's legal for a real estate licensee to solicit business from a "For Sale by Owner" seller. If the FSBO seller agrees that the licensee will help sell the property by advertising it on the MLS and elsewhere, in exchange for a fee, then the seller and licensee would simply enter into a listing agreement. (in addition, the other three options can be discarded via process of elimination. Undisclosed dual agencies, failure to supervise employees, and blind ads are all illegal.)