Answer:
Entry C.
Explanation:
According to the correct way of listing the works cited, the last name of the author will come first, followed by the other names i.e. the first name and if available, the second name. (Horton, Michael, no second name available)
Then, the name of the work follows, with the correct way of punctuation/ capitalization. (Letter to the Author).
Followed by the publication date and the year, if provided. Finally, the remaining details such as the publishers or printers or anything related will be in the end.
Thus, the correct way of citing the work will be
Horton, Michael. Letter to the Author. 12 Jan. 2010. TS.