Concept:Dirt or dust on the mouse rollers or sensor reduces its ability to track movement correctly.Explanation:When the mouse is dirty, its internal parts cannot detect motion properly.This causes the cursor on the screen to move in an irregular and uncontrolled way.Instead of following the movement of the mouse smoothly, it may jump or drift.Therefore, an erratic pointer is a clear sign of a dirty mouse.Answer:D. pointer moves erratically