In this sentence, the relative pronoun that should introduce the clause The Adventures ... published to make a relative clause modifying year. Also, the singular title of the novel demands a singular verb: for example, one would say, "The Adventures of Huckleberry Finn is (not "are") a great book." Only C, the best choice, satisfies both requirements. Choices A and D incorrectly substitute as for that to introduce the relative clause. Choice A also mistakes the novel title for a plural (were published). B confuses meaning (written in the same year of publication as). E creates a similar confusion of meaning, and both D and E are awkward and imprecise because that is too far away from its referent (letter) to be clear.