Wooden pencil casing and davy lamp: what they have in common

1. Step 1. Wooden pencil casing — is part of — Pencil. A cedar or lime-wood casing.
2. Step 2. Pencil — is made of — Graphite. The lead is graphite mixed with clay.
3. Step 3. Graphite — is a kind of — Carbon. A form of carbon.
4. Step 4. Carbon — includes — Coal. Mostly carbon.
5. Step 5. Coal — uses — Coal mine. Extraction.
6. Step 6. Coal mine — uses — Davy lamp. Protection against methane explosions.

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