Detailed Instructions: 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.
Problem:Question: How long had Mehmed been a Sultan when his forces conquered Constantinople? Passage:This is a list of campaigns personally led by Mehmed II or Sultan Mehmed the Conqueror (30 March 1432 – 3 May 1481) (Ottoman Turkish: محمد ثانى, Meḥmed-i s̠ānī; Turkish: II. Mehmet; also known as el-Fātiḥ, الفاتح, "the Conqueror" in Ottoman Turkish; in modern Turkish, Fatih Sultan Mehmet; also called Mahomet II in early modern Europe) was Sultan of the Ottoman Empire twice, first for a short time from 1444 to September 1446, and later from February 1451 to 1481. At the age of 21, he conquered Constantinople and brought an end to the Byzantine Empire, transforming the Ottoman state into an empire. Mehmed continued his conquests in Asia, with the Anatolian reunification, and in Europe, as far as Bosnia and Croatia. Mehmed II is regarded as a national hero in Turkey, and Istanbul's Fatih Sultan Mehmet Bridge is named after him.
 Links: a. Fall of Constantinople b. Ottoman Empire c. Ottoman Empire d. Mehmed the Conqueror
Solution:
a