Definition: In this task, you're given an article and an answer. Your task is to generate the fill-in-the-blank question for this answer based on the given article. The blanks are always at the end of the question, and can be filled with more than one word or phrase.
Input: Article: Mark Twain, the famous American writer, liked to play jokes on others. But once a joke was played on him. One day Mark Twain was invited to give a talk in a small town. At lunch he met a young man, one of his friends. The young man said that he has an uncle with him. He told Twain that his uncle never laughed or smiled, and that nobody and nothing was able to make his uncle smile or laugh. "You bring your uncle to my talk tonight," said Mark Twain. "I'm sure I can make him laugh" That evening the young man and his uncle sat in the front. Mark Twain began to speak. He told several funny stories. This made everyone in the room laugh. But the man never even smiled. Mark Twain told more funny stories, but the old man still kept quiet. Mark Twain told his funny stories. Finally he stopped. He was tired and quite disappointed. Some days later, Mark Twain told another friend of his about what had happened. "Oh," said his friend. "I know that old man. He's been deaf for years." 
 Answer: others

Mark Twain liked to play jokes on  _  .