Which of the following accurately describes the M240B machine gun?

The M240B machine gun is characterized as a belt-fed, air-cooled, gas-operated, fully automatic machine gun. This description provides a clear understanding of its operational features and design.

Being belt-fed means that it uses a belt of ammunition, which allows for sustained fire without the need for frequent reloading, making it effective in combat situations. The air-cooled feature indicates that it relies on the surrounding air to dissipate heat generated during firing, in contrast to a water-cooled system which requires more complex logistics for operation. The gas-operated mechanism refers to the way the weapon utilizes the gas produced by firing the round to cycle the action and prepare the next round for firing, aiding in a fully automatic mode of operation that can deliver continuous fire as long as the trigger is held down.

Together, these features illustrate why option B accurately captures the essential characteristics of the M240B machine gun, ensuring that it is appropriately classified in terms of its functionality and application on the battlefield.