Which of the following statements about emissions systems is correct?

Emissions systems can degrade over time, and this degradation can lead to increased emissions from the vehicle. Over time, components of the emissions control system, such as catalytic converters, oxygen sensors, and exhaust gas recirculation systems, may wear out or become less effective due to contamination, physical damage, or exposure to heat and chemicals. When these components do not function optimally, the vehicle may produce higher levels of pollutants, violating emission standards. Regular maintenance and timely repairs are crucial in ensuring the emissions system operates effectively to minimize environmental impact.

The other options do not accurately reflect the characteristics of emissions systems. Older vehicles generally have less effective emissions systems compared to newer technology, which is designed to be more efficient. Also, vehicles vary widely in their emissions systems based on the manufacturer, model, and year, so it's incorrect to say that all vehicles have identical systems. Finally, while newer vehicles often have advanced emissions controls, they can still require emissions testing depending on local regulations and the specific vehicle's age, making the assertion that they "never" require testing inaccurate.