Concept:A safety precaution is an action that prevents harm when using an electronic appliance.Explanation:Overloading a socket outlet can cause overheating and fire, so it is not safe.Plugging an appliance in before cleaning risks electric shock.Switching off an appliance after use prevents overheating and accidental operation, so it is the correct safety precaution.Using an appliance before reading instructions can lead to misuse and injury.Answer:C. switching off appliance after use.