In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: What year did the Steelers appear in their first Super Bowl? Passage:The Pittsburgh Steelers compete in the National Football League (NFL) as a member club of the American Football Conference (AFC) North division. Founded in 1933, the Steelers are the oldest franchise in the AFC; seven franchises in the National Football Conference (NFC) have longer tenures in the NFL. The team struggled to be competitive in its early history, posting winning records in just 8 of its first 39 seasons. Since the AFL–NFL merger in 1970, however, it has appeared in eight Super Bowls and one of only two teams, along with the New England Patriots have won the Super Bowl six times. The six championships place the Steelers fourth in the league in terms of total championships (including those prior to the first Super Bowl), trailing only the Green Bay Packers (13 championships), the Chicago Bears (9) and the New York Giants (8). The club's 15 AFC Championship Game appearances are second all-time, behind the Patriots (16). In addition, they have hosted the second-most conference championship games (11) than any franchise in either conference, and are tied for second with the Dallas Cowboys and Denver Broncos with eight Super Bowl appearances; the Patriots currently hold the record of eleven appearances, as of 2019.
 Links: a. National Football Conference b. National Football League c. Super Bowl d. Pittsburgh Steelers
d