Graphite pencil lead and telephone: what they have in common

1. Step 1. Graphite pencil lead — is part of — Pencil. A mixture of graphite and clay.
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 — is material for — Hearing aid. The first hearing aids used a carbon microphone.
5. Step 5. Hearing aid — evolved from — Telephone. The first electric hearing aids were built from telephone components.

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