30. Instead of we eat at home, we went to the restaurant. 31. I was listening to the radio when the door bell ring. 32. Smoking is harmful not only to smokers so to non-smokers. 33. Before the combine harvester had invented farmers had to cut and thresh rice by hand. 34. John said he will invite some of his friends for dinner so Mary had to buy some more food and drink. 35. Since fireworks are danger, many cities have laws preventing businesses from selling. 36. Let you and I consider the problems carefully. 37. He has learnt to drive when he was twenty. 38. Open the letter from her mother, she felt very happy. 39. Many scientists have tried to unlocking the genetic code. 40. Before go out , remember to turn off the lights. 42. I was walking along the road when I realized that there has been a man following me. 43. Peter has written the composition for 3 hours and he has not finished it yet. 44. Most lasers are be used in medical and scientific fields. 45. Please arrive on time in order to we will be able to start the meeting punctually minh dang can gap giup minh voi !