Which assembly houses the trigger assembly, sear, hammer assembly, selector lever, rifle grip, bolt catch, and buttstock assembly?

The lower receiver and buttstock assembly is the correct answer because it encompasses several critical components that contribute to the firearm's operation and functionality. This assembly contains the trigger assembly, which is essential for firing the weapon, as well as the sear and hammer assembly, which work together to release the firing pin when the trigger is engaged. Additionally, the selector lever, responsible for switching between firing modes, is housed within this assembly.

The rifle grip is part of the lower receiver, providing the shooter with a stable hold for aiming and firing. The bolt catch, which allows the shooter to hold the bolt open after the last round is fired, is also integrated into this assembly. Finally, the buttstock assembly is essential for bracing the weapon against the shooter's shoulder, contributing to comfort and control during firing.

Other options do not encapsulate the full range of components mentioned. The upper receiver primarily houses the barrel and bolt assembly, while the gas block assembly pertains to the gas system responsible for cycling the action. The trigger housing is a specific part of the trigger mechanism rather than the entire assembly that includes all the mentioned components. Thus, the lower receiver and buttstock assembly is key to understanding how the firearm operates in relation to its firing mechanism and overall