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！