Final answer:
Driving in the mountains, idling for extended times, and city driving all affect fuel usage estimations, which makes 'D. All of the above' the correct answer. These situations increase fuel consumption beyond ideal conditions due to additional energy demands, frequent stopping, and starting.
Step-by-step explanation:
The factors that could affect your fuel usage estimations are:
Driving in the mountains
Idling for an extended period of time
City driving
All of the above
Hence, the correct answer is D. All of the above. Driving in the mountains requires more energy due to the increased need to overcome gravitational forces, thus increasing fuel consumption. Idling for an extended period of time wastes fuel as the engine is running but the vehicle isn't moving.
City driving often involves frequent stopping and starting, which also increases fuel consumption due to acceleration requirements. All these scenarios require more fuel than estimated under ideal driving conditions which assume constant speed and minimal stop-and-go circumstances.
Additionally, other factors such as the efficiency of the car, extreme temperatures, or unexpected events (like a discovery of new oil reserves or geopolitical issues affecting oil supply) can further influence fuel usage. For example, a cold winter requires more energy to warm up the car and maintain engine performance, hence affecting fuel economy.