Which of the following is a method to restrict a fire?

Restricting a fire involves taking measures to limit its spread and impact. Closing doors is an effective way to contain a fire within a specific area. This action helps to prevent the fire from gaining access to additional combustible materials and isolates the heat and smoke, creating a barrier that can hinder the fire's progression. By reducing airflow and containing the fire, closing doors serves as an important control measure in fire safety protocols, thereby protecting other areas of the structure and allowing for more effective firefighting efforts.

Other methods, such as extinguishing the fire or smothering it with a blanket, may extinguish flames but do not necessarily limit the fire's potential to spread once it becomes active. Removing oxygen can be a part of extinguishing tactics but isn't a method of restriction in terms of containing the fire within an area. Thus, closing doors stands out as a fundamental action in fire safety practice aimed directly at restricting a fire's spread.