19. On arriving at home I (find)that she (just/leave)a few minutes before. 20. When we (arrive) in London tonight, it (probably/rain). 21. it (rain) hard. We can't do anything until it (stop). 22. Last...

Here are the correct verb forms: 19. On arriving at home I found that she had just left a few minutes before. 20. When we arrive in London tonight, it will probably rain. 21. It is raining hard. We can't do anything until it stops. 22. Last night we were watching TV when the power failed. 23. I sat down for a rest while the shoes were being repaired. 24. Halfway to the office, Paul turned round and went back home because he had forgotten to turn the gas off.