The conversation between human and AI assistant.
[|Human|] Generate two ways to classify the following objects: paper, pencil, eraser, ruler.
[|AI|] 1) Writing Instruments and Accessories:
- Writing Instruments: Pencil
- Accessories: Paper, Eraser, Ruler

2) Stationery Items by Physical Properties:
- Flexible: Paper
- Rigid: Pencil, Eraser, Ruler.
[|Human|] 
Generate two ways to classify the following objects: paper, pencil, eraser, ruler.