What type of system helps to manage the air-fuel mixture in modern engines?

The fuel injection system is the correct choice because it is the modern method used to deliver fuel to the engine's combustion chamber in a precise manner. This system atomizes the fuel and mixes it with air at the optimal ratio for combustion, ensuring efficient engine operation and performance.

Fuel injection systems use electronic controls to monitor various parameters such as engine speed, load, and temperature, allowing for dynamic adjustments to the air-fuel mixture based on the demands of the engine. This results in improved fuel efficiency, reduced emissions, and enhanced power output.

In contrast, carburetor systems, while historically significant, are largely outdated in modern engines, having been replaced by more sophisticated and efficient fuel injection systems. Mechanical linkage systems refer to the physical connections that can control throttle positions but do not manage the air-fuel mixture directly. Gravity-fed systems describe an older method of fuel delivery that lacks the precision and control provided by fuel injection, making them unsuitable for contemporary engine designs.