This task is about writing a correct answer for the reading comprehension task. Based on the information provided in a given passage, you should identify the shortest continuous text span from the passage that serves as an answer to the given question. Avoid answers that are incorrect or provides incomplete justification for the question.
Q: Passage: Martin Luther, a German monk, started the German Reformation by posting 95 theses on the castle church of Wittenberg on October 31, 1517. The immediate provocation spurring this act was Pope Leo X’s renewal of the indulgence for the building of the new St. Peter's Basilica in 1514. Luther was challenged to recant his heresy at the Diet of Worms in 1521. When he refused, he was placed under the ban of the Empire by Charles V. Receiving the protection of Frederick the Wise, he was then able to translate the Bible into German. Question: What was Martin Luther's response when challenged to recant his heresy?
A: 
he refused