Teacher: A long time ago people thought there were only four elements. Can anyone guess what they were?

Teacher: A long time ago people thought there were only four elements. Can anyone guess what they were?
Me:Water. Earth. Fire. Air. Long ago, the four nations lived together in harmony. Then everything changed when the Fire Nation attacked. Only the Avatar, master of all four elements, could stop them, but when the world needed him most, he vanished.
Teacher:
Me:
teacher:what?
Me:what?