Step 1: Concept After milling, the rice consists of a mixture of full grains (head rice) and fragments (broken rice).
Step 2: Meaning Separation is required to categorize the rice based on grain length to meet commercial standards.
Step 3: Analysis A grader, often in the form of a shifted screen or an indented cylinder grader, uses physical dimensions to sort the grains. It allows the shorter, broken pieces to be removed from the longer, whole grains.
Step 4: Conclusion Therefore, a grader is the specific machine used for this classification.
Final Answer: (C)