Which of the following is not considered to be "tampering"?

Defective parts are deemed not to be an act of tampering because they can occur naturally over time due to wear and tear or manufacturing defects, rather than being a deliberate action to modify or disable emissions control systems. Tampering typically refers to intentional alterations made to a vehicle's emissions control systems in order to circumvent emissions standards. In contrast, removing a catalytic converter, altering emissions control devices, or adjusting the fuel-air mixture would all consist of intentional modifications aimed at affecting emissions, which are considered tampering. Thus, defective parts, which can emerge without malicious intent, do not fall under the scope of tampering.