1. My sister gave me a new pair of jeans on my fìteenth birthday.
-> I was given a new pair of jeans by my sister on my fìteenth birthday.
-> A new pair of jeans was given to me by my sister on my fìteenth birthday.
2. The workers are building a supermarket on our street. 
-> A supermarket is being built on our street by the workers .
3. The zoo keepers feed the animals twice a day.
-> The animals are fed twice a day by the zoo keepers.
4. They have sold their car to pay their debt.
-> Their car has been sold (by them) to pay their debt.
5. We are going to grow flowers in the front garden.
-> Flowers are going to be grown in the front garden by us.