7 предложений с Passive Voice

1. A new fashionable trading centre has been built in the centre of our city recently. 2. These letters have already been signed by our boss and they must be sent immediately. 3. My parents were invented to the restaurant to celebrate their friend\'s birthday. 4. Many new modern houses are built in our town every year. 5. You will be helped in your work if it\'s too difficult. 6. The dinner was being cooked when our guests arrived. 7. By 6 o\'clock in the evening all his homework had already been done.