Если можно использовать только третье условное, то так:
1) If she had had a car, she could have driven there.
2) Had I known she was the examiner, I wouldn't have made a silly joke.
3) I might have gone upstairs if I hadn't been afraid of the dark.
4) If she hadn't been nervous, she wouldn't have made a mistake.
5) If the other pupil hadn't laughed at me, I wouldn't have cried.