1.
1) We have finished our work.
2) They have bought a new house.
3) She has not seen her sister.
4) They have not phoned the doctor.
2.
1. the youngest
2. the worst
3. the funniest
4. the tallest
5. the best
6. the most beautiful
3.
1) has washed
2) have moved
3) have bought
4) has lost
5) has broken
6) have taken
7) has stopped
8) has locked
9) have brought