Trolleybus e electrical telegraph: o que têm em comum

1. Passo 1. Trolleybus — tem como parte — Pneumatic tyre. Runs on tyres.
2. Passo 2. Pneumatic tyre — tem como parte — Tyre tread. A tread.
3. Passo 3. Tyre tread — é feito de — Carbono. With carbon black for strength.
4. Passo 4. Carbono — é material para — Hearing aid. The first hearing aids used a carbon microphone.
5. Passo 5. Hearing aid — evoluiu de — Telephone. The first electric hearing aids were built from telephone components.
6. Passo 6. Telephone — evoluiu de — Electrical telegraph. The telephone grew out of attempts to send several signals over telegraph lines (the “harmonic telegraph”).

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