posted by rfvv .
1. Which country's flag is this?
1-1. This is America's flag.
1-2. This is an American flag.
2. Which country use this national flag?
2-1. Japan does.
2-2. Japan use it.
3. In which country is this flag used?
3-1. In France.
(Are the questions and answers all correct? Do you have better questions related to national flags?)
All are fine except 2 and 2-2. In both of those sentences the verb needs to be in 3rd person singular form: "uses."