16. On arriving at home I (find) found that she had just (leave) left a few minutes before.

17. When we (arrive) arrive in London tonight, it will probably (rain) be rainning

18. It (rain) is raining hard. We can't do anything until it (stop) stop
19. Last night we were watching TV when the power failed

20. That evening we (stay) stayed up to talk about the town where he (live) has lived for some years.