Differential and aerosol can: what they have in common

1. Step 1. Differential — is part of — Truck. Differentials in the drive axles.
2. Step 2. Truck — evolved into — Ambulance. A special-purpose vehicle.
3. Step 3. Ambulance — has part — Ventilator. Medical equipment.
4. Step 4. Ventilator — has part — Valve. Valves.
5. Step 5. Valve — is part of — Aerosol can. A valve.

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