Classification – Natural substances vs man-made machine: choose the odd one out. Three are naturally occurring materials or living things; one is a manufactured machine. Which option does not belong? Options: Wood, Stone, Tree, Engine.

Introduction / Context:
Basic general-knowledge classification often separates natural entities from manufactured artifacts. Here, three entries are natural (materials or a living organism), contrasted with one man-made machine.

Given Data / Assumptions:

• Wood: natural material from trees.
• Stone: natural geological material.
• Tree: natural living organism.
• Engine: manufactured machine/device.

Concept / Approach:
Group items by origin: natural vs man-made.

Step-by-Step Solution:
Tag Wood/Stone/Tree as natural.Tag Engine as man-made machine.Therefore, Engine is the odd one out.

Verification / Alternative check:
Cross-check typical store or encyclopedia categories: the first three are not manufactured devices.

Why Other Options Are Wrong:
Wood/Stone/Tree: Each is natural in origin and fits the majority group.

Common Pitfalls:
Over-focusing on “tree vs wood” relation; origin (natural vs manufactured) is the decisive axis.

Final Answer:
Engine