Tìm lỗi sai và sửa lại 40. Using solar energy instead fossil fuels can help reverse the effects of global warming. 41. Many people living in rural areas use biogas to cook, and heating. 42. Wind power is clean, abundant, widely available, and environmental friendly. 43. When you were a child, you used to go to school on foot, weren't you? 44. Friday night, a friend of our from college came up to see us. 45. Another Japanese city, Osaka, also has a very large population with 20.5 million.