Sure! Here are the correct verb forms for each sentence:

1. If the doctor **had not noticed** the defect when I was a child, I **would be** practically blind by now.
2. Frank (be) **wouldn't have known** if that boy (not know) **didn't know** how to do artificial respiration.
3. Tell him to ring me up if you (see) **see** him.
4. If I lend you $10 when you (repay) **repay** me?
5. If you (not sneeze) **hadn't sneezed**, he wouldn't have known that we were there.
6. I (not eat) **didn't know** if I (know) **had known** that there was ginger in it.
7. She (be) **would (be)** a lot faster if her shoes didn’t have such high heels.
8. What (happen) **happens** if I (press) **press** this button?
9. I could repair the roof myself if I (have) **had** a long ladder.
10. I should have voted for her if I (know) **had known**, a vote then.
11. If I were sent to prison, would you (visit) **visit** me?
12. What you (do) **would you do** if you found a burglar in your house?
13. If he worked more slowly (he not make) **he wouldn't make** so many mistakes.
14. What will happen if my parachute (not open) **doesn't open**?
15. I shouldn’t have believed it if I (not see) **hadn't seen** it with my own eyes.
16. I (take) **would take** a taxi if I (realize) **had realized** that it was such a long way.
17. Someone offered to buy you one of those rings, which (choose) **you chose**?
18. If you (wear) **had worn** a false beard nobody would have recognized you.
19. If you (listen) **had listened** to the traffic report on the radio this morning, we (not sit) **would not be sitting** here in this jam.
20. We (live) **would live** in London if we (not find) **hadn't found** someone to buy our house last year.
21. Just think, if I (take) **had taken** that job with the export company, I (live) **would be living** in Sao Paulo now, not Manchester!

Feel free to ask if you need further assistance!