Teacher: What are the four elements of nature?

  Student: Fire, air, earth, and….

  Teacher: And what? Just think it over. What do you wash your hands with?

  Student: Soap!

  老师：什么是自然界的四大元素？

  学生：火，空气，土，和….

  老师：和什么？好好想想，你用什么洗手？

  学生：肥皂！