1. They are able students.
Альтерн.: Are they or we able students?
Разделит.: They are able students, aren't they?
2. My brother gives lectures in universities.
Does my brother give lectures in universities or secondary schools?
My brother gives lectures in universities, doesn't he?
3. She spent a lot of time in the country last year.
Did she or he spend a lot of time in the country last year?
She spent a lot of time in the country last year, didn't she?