What type of air is ducted around the engine to produce thrust?

Bypass air is the correct type of air that is ducted around the engine to produce thrust in a high-bypass turbofan engine configuration. In this type of engine, a significant portion of the air that enters the engine bypasses the combustion section and travels through a large duct surrounding it. This bypassed air accelerates through a high bypass ratio fan, and its thrust is generated primarily due to the mass flow of air propelled rearward, which is far more efficient than the thrust produced by the combustion process alone.

The design of high-bypass engines is intended to maximize efficiency and minimize noise, making them commonly used in commercial aviation. By using a larger volume of bypass air, the engine can produce more thrust at a lower speed and reduced fuel consumption, resulting in better overall performance for the aircraft.

In contrast, other types of air mentioned in the options serve different functions. Combustion air is the air that mixes with fuel in the combustion chamber to generate thrust, while cooling air is used to maintain optimal operating temperatures in various engine components. Exhaust air refers to the gases expelled after combustion, contributing to thrust in some engine designs, but it's not ducted around the engine in the same manner as bypass air.