The correct answer is C) he thinks they have been unfairly imprisoned and oppressed.
In chapter 8, Don Quixote frees the prisoners he meets because he thinks they have been unfairly imprisoned and oppressed.
Don Quixote sees that the prisoners and handcuffed and wearing chains. The prisoners are there because they are poor people that He thinks that is unfair for poor people who are forced into jail to serve the king for the committed crimes. He is upset and comments this with Sancho Panza. The prisoners are kept in the Galeras, the Spanish word that the author uses to name the galleys.
Miguel De Cervantes Saavedra wrote “The Ingenious Gentleman Sir Quixote de la Mancha.” The first part was written in 1605 and the second part in 1615. It is the most important piece of literature of the Spanish Golden Age.