Odd One Out — Paper, Wood, and Leather differ in flexibility and processing; Wool is a soft fibrous material. Alternatively, by rigidity, Wood alone is rigid compared to the other three. Choose the odd item using a clear, single property.

Introduction / Context:
Material classification can be made via mechanical properties such as rigidity/flexibility. A single consistent criterion should produce one clear exception.

Given Data / Assumptions:

• Paper: flexible sheet (bends/tears easily).
• Wool: soft fibrous textile (high flexibility).
• Leather: flexible processed hide (pliable).
• Wood: generally rigid structural material (stiff, not readily flexible in thin sections without special processing).

Concept / Approach:
Use flexibility/rigidity as the discriminator. Select the only predominantly rigid material in common forms of use.

Step-by-Step Solution:
Paper → flexible.Wool → flexible (fibers).Leather → flexible (sheet).Wood → rigid → outlier.

Verification / Alternative check:
Processing origin (plant vs animal) yields a 2–2 split (paper/wood plant, wool/leather animal). Rigidity cleanly isolates wood as the single rigid common-use material.

Why Other Options Are Wrong:

• Paper, Wool, Leather: typically flexible in normal usage thicknesses.

Common Pitfalls:
Mixing multiple criteria (origin and processing) that do not produce a unique outlier. Stick to one consistent property.

Final Answer:
Wood