What maintenance task is essential for ensuring the longevity of a school bus's battery?

Answer: B — Regular cleaning of terminals and checking for corrosion

Regular cleaning of the terminals and checking for corrosion is vital for ensuring the longevity of a school bus's battery. Over time, battery terminals can accumulate dirt, grime, and corrosion, which can inhibit the flow of electrical current. This can lead to starting problems or electrical failures. By keeping the terminals clean and free from corrosion, you help maintain optimal conductivity, ensuring that the battery can effectively deliver power to the bus’s electrical systems. The other tasks mentioned do not directly contribute to battery maintenance. Changing the oil regularly is important for the engine's health, calibrating the speedometer is related to the accuracy of speed readings, and replacing tires annually pertains to safety and handling rather than battery performance. While all of these maintenance tasks are important for the overall operation of the bus, it is the cleaning of terminals and corrosion checking that specifically targets the battery's functionality and longevity.