What could contribute to poor fuel economy?

The correct choice highlights various factors that can directly impact a vehicle's fuel economy. Worn spark plugs can lead to incomplete combustion, meaning that not all the fuel is effectively utilized, which adversely affects fuel efficiency. Low tire pressure increases rolling resistance, requiring more energy to move the vehicle, and thus decreasing fuel economy. A clogged air filter restricts airflow to the engine, which can also lead to inefficient combustion and poor performance.

Each of these components works together to ensure optimal engine performance; therefore, if any one of them is compromised, it can result in noticeable fuel efficiency issues. High-quality fuel, regular engine cleaning, and updated navigation systems, on the other hand, are generally seen as improvements that may enhance performance or convenience but do not directly contribute to significant decreases in fuel economy when properly managed.