Q: 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: Which of the two characters that were additional features to Superman was introduced first? Passage:Gradually, the size of the issues was decreased as the publisher was reluctant to raise the cover price from the original 10 cents, so there were fewer stories. For a while, Congo Bill and Tommy Tomorrow were the two features in addition to Superman. Writer Robert Bernstein and artist Howard Sherman revamped the "Congo Bill" backup feature in issue #248 (January 1959) in a story wherein the character gained the ability to swap bodies with a gorilla and his strip was renamed Congorilla. The introduction of Supergirl by Otto Binder and Al Plastino occurred in issue #252 (May 1959). Following this debut appearance, Supergirl adopted the secret identity of an orphan "Linda Lee" and made Midvale Orphanage her base of operations. In Action Comics #261 (February 1960), her pet cat Streaky was introduced by Jerry Siegel and Jim Mooney. Supergirl joined the Legion of Super-Heroes in issue #276 and acted for three years as Superman's "secret weapon," until her existence was revealed in Action Comics #285 (January 1962). In the view of comics historian Les Daniels, artist Curt Swan became the definitive artist of Superman in the early 1960s with a "new look" to the character that replaced Wayne Boring's version. Bizarro World first appeared in the story "The World of Bizarros!" in issue #262 (April 1960). Writer Jim Shooter created the villain the Parasite in Action Comics #340 (Aug. 1966).
 Links: a. Curt Swan b. Jim Shooter c. Congorilla d. Legion of Super-Heroes
A:
c