6. By the time the policeman arrived, the robber had escaped.

7. Have you ever known to New York at all ? (????)

8. My family was having dinner when she visited us.

9. We haven't seen your sister since May.

6. That policeman arrived too late so the robber escaped.

-> By the time the policeman arrived, the robber escaped.

7. Do you know New York at all?

-> Have you ever known to New York at all ? 

8. When did you buy your laptop?

-> How long have you bought your laptop?

9. Her visit interrupted my family's dinner.

-> My family was having dinner when she visited.

10. We last saw your sister in May.

-> We haven't seen your sister since May.