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: How old was the German king Thomas alerted of his ascension when Tvrtko died? Passage:Tvrtko II died in November 1443. The Stanak approved his choice of heir, and Thomas was duly elected king by 5 December. Like his predecessors, he added the royal name Stephen to his own. However, the kingdom's most powerful magnate, Grand Duke Stjepan Vukcic Kosaca, refused to accept Thomas as king, and announced his support for Radivoj. The authorities of the neighbouring Republic of Ragusa immediately expressed concern about the situation. Kosaca and Radivoj appealed to Ragusa not to recognize Thomas as king, but to no avail. Simultaneously, Hermann's grandson Ulrich II pressed his claim to the Bosnian throne and tried to gather support among Thomas's opponents. Because of this, Thomas hastened to send word of his accession to foreign rulers, including the German king Frederick IV, Ulrich's rival, and Ragusan and Venetian authorities, hoping to receive recognition. Ulrich was occupied with the feud waged against him by Frederick, as well as with the succession struggle in Hungary, where he had taken side with his cousin, queen dowager Elizabeth of Luxembourg and her infant son Ladislaus against the reigning monarch Vladislav I, leaving Thomas ample space of maneuver.
Links: a. Frederick III, Holy Roman Emperor b. Frederick III, Holy Roman Emperor c. Ulrich II, Count of Celje d. Frederick III, Holy Roman Emperor
A:
a