1. Is Mike your friend? - No, he isn't. Mike is not your friend. Mike is his friend.
2. Are they engineers? - No, they aren't. They are not engineers. They are cleaners.
3. Are these codes? - No, they aren't. These are not codes. These are letters.
4. Is it your file? - No, it isn't. It is not your file. It is my friend's file.
5. Is this a display? - No, it isn't. This is not a display. This is a TV set.
6. Is this computer yours? - No, it isn't. This computer is not yours. It is my teacher's computer.
7. Is he a schoolboy? - No, he isn't. He is not a schoolboy. He is a student.