Complete the sentences with the correct form of the verbs given.

1) If space tourism ... around when my grandad was alive, he'd definitely have gone on a flight.
2) If the driving test ... so difficult, there would be more accidents on the roads.
3) Scientists usually ... more accurate results if they repeat experiments several times.
4) It would be illegal if they ... experiments on humans, so they are using rats.

5) They ... a breakthrough sooner if a fire in the laboratory hadn't destroyed their experiments.
6) You are at risk of getting yellow fever if you ... to many parts of Africa.

7) If it ... for past pioneers, their research wouldn't have been possible.

8) If you ... plants, they die.

9) If my sister gets a cold, I usually ... it, too.
10) If it's warm this afternoon, I ... home.
11) If I ... , I would have passed the exam.
12) If my brother ... his final exams, he'll be a doctor next month.
13) If he had come to school yesterday, he ... an exam.
14) If I ... better at sport, I'd play more.
15) If I had a private jet, I ... around the world.