In much the same way as an engine runs on diesel fuel, the human body runs on:

The human body primarily runs on glucose, making it the most appropriate answer in this context. Glucose serves as a key source of energy, particularly for the brain and muscles during physical activity. When carbohydrates are consumed, they are broken down into glucose, which then enters the bloodstream and is used by cells for energy.

While oxygen is essential for aerobic respiration and is needed to efficiently convert glucose into energy, it is not a fuel source in the same manner as glucose. Similarly, fats and proteins serve roles in energy production but are typically processed and utilized as secondary fuel sources. Fats can be broken down into fatty acids and utilized for energy, especially during prolonged exercise, while proteins are mainly used for tissue repair and building rather than as a direct energy source.

Thus, glucose is the primary fuel that our bodies rely on similarly to how an engine utilizes diesel fuel for operation, making it the most fitting answer for this analogy.