Roman concrete and truck: what they have in common

1. Step 1. Roman concrete — is material for — Dam. Ancient dams; modern ones are made of concrete.
2. Step 2. Dam — is part of — Hydroelectric power station. The dam creates the head of water.
3. Step 3. Hydroelectric power station — has part — Electric generator. Generators.
4. Step 4. Electric generator — is part of — Diesel locomotive. The generator powers the traction motors.
5. Step 5. Diesel locomotive — has part — Air brake. Air brakes.
6. Step 6. Air brake — is part of — Truck. Air brakes, as on trains.

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