The correct answer is "combatir." This is because "combatir" is a verb in Spanish that means "to fight" or "to combat." It is the most appropriate choice among the given options as it directly relates to the concept of fighting or engaging in a battle. The other options, such as "alojar" (to lodge), "establecer" (to establish), "llenar" (to fill), and "componer" (to compose), do not have the same meaning or association with fighting.