Stretcher spreader bars and piston pump: what they have in common

1. Step 1. Stretcher spreader bars — is part of — Stretcher. They keep the canvas taut.
2. Step 2. Stretcher — is part of — Ambulance. A stretcher.
3. Step 3. Ambulance — evolved from — Truck. A special-purpose vehicle.
4. Step 4. Truck — has part — Diesel engine. A diesel engine.
5. Step 5. Diesel engine — has part — Cylinder. Cylinders.
6. Step 6. Cylinder — is part of — Piston pump. The piston moves in a cylinder.

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