a)
1. If it rains, we will stay at home.
2. If you don’t know the way, I will pick you up.
3. My mum will bake a cake if you come to see us.
4. They shall comes to his party if he invites them.
5. I will visits my grandparents if I have a long holiday.
 b) 
1. If you studied harder, you could get better marks in your tests.
2. If I were a rich, I would travel around the world.
3. She came to the market with us if she hadn’t to work.
4. We would sent you a message if we geted to the city.
5. I should call you back if I arrived at home.