Construct a question about the world of Avatar: The Last Airbender.
What are the four nations in the world of Avatar: The Last Airbender and their corresponding elements?
Complete the following task based on the instruction and optional input provided.### Instruction:
Construct a question about the world of Avatar: The Last Airbender.

### Output:
What are the four nations in the world of Avatar: The Last Airbender and their corresponding elements?