Blast furnace and modem: what they have in common

1. Step 1. Blast furnace — uses — Coke. The fuel and reducing agent is coke (formerly charcoal).
2. Step 2. Coke — is made of — Carbon. Coke is almost pure carbon: everything else is baked out of the coal.
3. Step 3. Carbon — is material for — Hearing aid. The first hearing aids used a carbon microphone.
4. Step 4. Hearing aid — evolved from — Telephone. The first electric hearing aids were built from telephone components.
5. Step 5. Telephone — is used in — Modem. It works over a telephone line.

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