17 meet ... looks
18 has been ... comes
19 found... has left
20 have arrived...  rained

16. have You (be) __been________here before? Yes, I (spend) ____spent______ my holidays here last year.
17. We have never (meet) ____met______ him. We don't know what he (look) _____looks_____ like.
18. The car (be) ____has been______ ready for him by the time he (come) ____comes______tomorrow.
19. On arriving at home I (find) ___found_______that she has just (leave) _____left_____a few minutes before.
20. When we (arrive) ____arrived______ in London tonight, it probably (rain) ____raining______.