Which best describes the M4 rifle?

The M4 rifle is best described as a 5.56mm, magazine-fed, gas-operated firearm that can operate in either semiautomatic or three-round burst modes. This designation highlights key features of the M4, such as its caliber, which allows for lightweight and manageable ammunition while maintaining effective range and stopping power. The magazine-fed design enhances the rifle's capacity for sustained fire, allowing soldiers to reload quickly in various combat scenarios.

Its gas-operated mechanism is crucial, as this system utilizes gas from the fired cartridge to cycle the action, enabling rapid follow-up shots without the need for manual operation. The inclusion of semiautomatic and three-round burst firing modes offers flexibility to the user, allowing for controlled shots in different tactical situations.

This comprehensive description aligns with the M4's role as a versatile, standard-issue weapon for many armed forces, particularly in the U.S. military. The other choices do not accurately reflect the characteristics of the M4, pointing to different types of rifles that serve different functions or uses altogether.