The correct answer is A los huéspedos en los balnearios les agradan las criadas y dejan una propina cuando ellos salen del hotel.
Explanation:
In this case we are faced with an indirect object pronoun. These are pronouns used to define to whom or for whom the action of a sentence is addressed.
To identify this type of pronouns we must ask the question to whom? or for whom?
Below I will write what are the indirect object pronoun of Spanish: