Which of the following can contribute to reduced fuel efficiency?

A clogged air filter can indeed contribute to reduced fuel efficiency. The air filter's role is to ensure that clean air enters the engine for optimal combustion. When the air filter is clogged, it restricts airflow, causing the engine to work harder to draw in air. This inefficiency means the engine burns more fuel to maintain power and performance, ultimately leading to lower miles per gallon and higher fuel consumption.

In contrast, maintaining a well-maintained engine, performing regular oil changes, and ensuring proper tire inflation all contribute positively to fuel efficiency. A well-maintained engine runs smoothly, a clean oil system allows for better lubrication and performance, and properly inflated tires reduce rolling resistance, all of which help in achieving better fuel economy.