What should you do after putting on the spare tire?

Answer: C — Ensure the lug nuts are secure

After putting on the spare tire, ensuring the lug nuts are secure is crucial for safe driving. This step is vital because lug nuts hold the tire firmly in place, and if they are not tightened properly, the tire could loosen while driving, leading to potentially dangerous situations such as losing a tire or experiencing poor handling of the vehicle. Properly securing the lug nuts ensures that the spare tire can support the vehicle's weight and function as intended. This process occurs before any other actions like test driving or checking the condition of the flat tire. While checking the flat tire may be important, it is secondary to ensuring that the spare is installed properly. Additionally, driving at high speed is not recommended immediately after changing a tire, as the spare may not be rated for high speeds or long distances, depending on its type. Therefore, the most critical and responsible action after installing a spare tire is to secure the lug nuts firmly.