1. It is his box.
Is it his box? --- Yes, it is.
2. There is a box under the chair.
----- Is there a box under the chair?
----- Yes, there is.
3. There were two boxes under the chair.
----- Were there two boxes under the chair?
----- Yes, there were.
4. The boxes were under the chair.
------- Were the boxes under the chair?
----- Yes, they were.