Final answer:
The extruder screw in a plastic extrusion machine moves the plastic materials through the barrel, which is the correct answer to the question.
Step-by-step explanation:
The extruder screw moves the plastic materials through the barrel of the machine. The correct answer to the multiple-choice question is C) Barrel. In the process of plastic extrusion, the raw plastic material is fed into the extruder, and an extruder screw pushes the material through the barrel, where it is heated and melted. The molten plastic is then forced out of the nozzle at the end of the barrel into the desired shape. The barrel is a critical component because it not only contains the plastic but also provides the chamber within which the plastic is melted and conveyed forward toward the nozzle.