What is the primary assembly that contains the sear in the M240?

The sear in the M240 is housed within the trigger housing, which is part of the weapon's firing mechanism. This component is essential for controlling the firing sequence of the machine gun. When the trigger is pulled, it interacts with the sear to either allow or prevent the bolt from moving forward to fire a round. The design of the trigger housing ensures that the sear is securely located, facilitating reliable and safe operation of the weapon.

While the other assemblies contribute to the overall function of the M240, they do not specifically contain the sear. For instance, the receiver assembly provides the structural framework and houses several mechanical components but is separate from the actual trigger mechanism. Therefore, the trigger housing is the correct answer as it specifically includes the sear, playing a crucial role in the operation of the firearm.