IN ONE WELL-KNOWN CITY, TRAFFIC POLICEMEN HAVE TO WEAR OXYGEN MASKS...

3. - File thứ 4: de_kiem_tra_lop_11-_sach_cu-_u8-9-10_311201817
File thứ 4: de_kiem_tra_lop_11-_sach_cu-_u8-9-10_311201817
3. In one well-known city, traffic policemen have to wear oxygen masks _____. A. in order to protect themselves from being injured B. because there are so many cars on the streets C. in spite of poisonous gases D. because of air pollution