Given the task definition, example input & output, solve the new input case.
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.
Example: Question: When did the operation during which the 704th dropped supplies to allied troops near Nijmegen begin? Passage: The group was occasionally diverted from strategic missions to carry out air support and interdiction missions. It supported Operation Overlord, the invasion of Normandy by attacking transportation targets, including bridges, along with airfields and strong points in France. On D Day, the squadron and the rest of the 446th Group led the first heavy bomber mission of the day. The 446th aided ground forces at Caen and Saint-Loduring July by hitting bridges, gun batteries, and enemy troops. During Operation Market Garden, the attempt to seize a bridgehead across the Rhine in the Netherlands, the 704th dropped supplies to allied troops near Nijmegen. It struck lines of communications during the Battle of the Bulge. During Operation Varsity in March 1945, it supplied ground and airborne troops near Wesel. The squadron flew its last combat mission on 25 April 1945 against Salzburg, Austria. The group had flown 273 missions and had lost 58 aircraft during the war,
. Links: a. Allies of World War II b. Wesel c. Operation Market Garden d. Air Support.
Output: c
The passage describes the 704th's actions during Operation Market Garden.

New input case for you: Question: How old was Basil Lekapenos when he joined on as the chamberlain of Constantine VII Porphyrogennetos? Passage:His role during the reign of his father is unknown. He first appears as the protovestiarios (chamberlain) of Constantine VII Porphyrogennetos (r. 913959), the legitimate emperor of the Macedonian dynasty, but it is unclear whether it was Romanos Lekapenos who appointed him to the post or whether Constantine VII gave it to him after Romanos' downfall. The contemporary Theophanes Continuatus reports that Basil was a loyal and dedicated servant of Constantine VII, and had a close relationship with Constantine's wife, and his own half-sister, Helena Lekapene. Following the deposition of Romanos Lekapenos in December 944, Basil supported Constantine VII when he regained power from Basil's half-brothers Stephen Lekapenos and Constantine Lekapenos in January 945, and was rewarded with senior titles and offices: in his seals and dedicatory inscriptions he is called a basilikos, patrikios, "paradynasteuon of the Senate" (likely a distortion indicating the combined titles of paradynasteuon and protos, "first", of the Senate), as well as megas baioulos (grand preceptor) of Constantine's son and heir, the future Romanos II (r. 959963). In ca. 947/8 he was raised further from protovestiarios to parakoimomenos (head chamberlain), in succession to Theophanes.
Links: a. Byzantine Senate b. Constantine VII c. Constantine Lekapenos d. Helena Lekapene
Output:
b