1. Who has been working on the report in the library all day long?
2. They have been working on the report in the library all day long, haven't they?
3. Where have they been working on the report all day long?
4. How long have they been working on the report in the library?
5. Have they been working on the report in the library all day long?
6. Have they been working on the report in the library or at home all day long?