题目

know tell invite be laugh Mark Twain, the famous American writer and a great master of humor, liked to play jokes on others. But once a joke was played on him.One day, Mark Twain 【1】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 had an uncle with him. He told Mark Twain that his uncle never laughed or smiled, and that nobody 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 【2】.”That evening the young man and his uncle sat in the front. Ma图1所示的四种现象中，属于光的折射现象的是（ ）