The correct answer is C) harder it is to extinguish. The longer an oil fire is permitted to burn, the more the fire will intensify and spread, making it increasingly difficult to extinguish. As the fire continues, the fuel source will increase, generating more heat and flames, which in turn makes the fire progressively harder to control and extinguish. Conversely, the other options are incorrect - the fire does not become easier to control or extinguish, nor is there less chance of reignition, as the fire grows in size and intensity over time.