Chuyển các câu chủ động sau sang dạng bị động. 1. In ancient times, people lit fires to use smoke as a signal over long distances. ________________________________________________________________________________________ 2. James Dyson invented Google Glass over a decade ago. ________________________________________________________________________________________ 3. People used radios to broadcast code messages during the Second World War. ________________________________________________________________________________________ 4. Most employers must pay the workers at least the federal minimum wage. ________________________________________________________________________________________ 5. A consumer group has found fake goats’ cheese for sale in supermarkets. ________________________________________________________________________________________ 6. Trans-fats which are bad for our hearts and cholesterol levels fill these low-fat foods. ________________________________________________________________________________________ 7. Have some scientists discovered a huge Blue whale colony in Sri Lanka? ________________________________________________________________________________________