Which of the following describes the operational behavior of the M16/A2?

The M16/A2 is described accurately as gas-operated, semi-automatic or three-round burst. This means that the rifle uses the energy from the gases produced when a round is fired to cycle the action of the weapon, automatically loading the next round into the chamber. The M16/A2 features a selectable firing mode, allowing the shooter to choose between semi-automatic fire, where one round is fired for each pull of the trigger, and a three-round burst mode, where the rifle fires three rounds automatically with a single pull of the trigger before requiring the trigger to be released and pulled again for additional bursts. This capability enhances the versatility of the weapon in various combat situations.

The other options are not consistent with the operation of the M16/A2. For example, describing the rifle as recoil-operated or lever-action does not reflect its actual mechanism, which does not rely on recoil alone or require manual cycling of the action like lever-action firearms. Additionally, spring-loaded and fully automatic descriptions do not apply, as the M16/A2 is not a fully automatic weapon by default and operates primarily through gas operation.