Electroencephalograph and truck: what they have in common

1. Step 1. Electroencephalograph — has part — Amplifier. Amplifiers.
2. Step 2. Amplifier — includes — Hi-fi amplifier. An amplifier.
3. Step 3. Hi-fi amplifier — has part — Transformer. The power supply is a transformer.
4. Step 4. Transformer — is part of — Defibrillator. Stepping up the voltage.
5. Step 5. Defibrillator — is part of — Ambulance. A defibrillator.
6. Step 6. Ambulance — evolved from — Truck. A special-purpose vehicle.

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