1. It (to be) hard for a fire man to know how a fire behaves, because so many things can affect it. 2. The strength and direction of the wind (to be) important factors. 3. Smoke (to be) a mixture that comes from burning of any kind of material, such as coal, wood, or petroleum. 4. After the fire (to be out), the fire man still have much work to do. 5. The heat-reflective suits (to be) fire resistant and coated with aluminum to reflect heat. 6. Radio (to be) important to the modern fire department. 7. The smallest unit of fire department (to be) a company of about 6 to 16 men.