Which building is it?

Based on the descriptions provided:

1. The largest building in the world is **C**. Boeing Everett Factory.
2. The oldest building in the world is **B**. Knap of Howar.
3. The tallest building in the world is **A**. Burj Khalifa.
4. The building with the fastest elevators is **A**. Burj Khalifa.
5. The building made entirely of stone is likely **B**. Knap of Howar.
6. The building that is like a small city with many facilities is **C**. Boeing Everett Factory.

If you need any more details or help, feel free to ask!