Answer:

3. I'm looking for your keys.

   Am I looking for your keys?

   I'm not looking for your keys.

4. We're selling the house.

   Are we selling the house?

   We're not selling the house.

5. You're working very hard.

   Are you working very hard?

   You're not working very hard.

6. He's washing the dishes.

   Is he washing the dishes?

   He's not washing the dishes.

7. They're drinking tea.

   Are they drinking tea?

   They're not drinking tea.

8. We're having a good time.

   Are we having a good time?

   We're not having a good time.

9. She's leaving him.

   Is she leaving him?

   She's not leaving him.

10. I'm going home now.

    Am I going home now?

    I'm not going home now.