Upper water reservoir and aeroplane: what they have in common

1. Step 1. Upper water reservoir — is part of — Carbide lamp. Water drips onto the carbide.
2. Step 2. Carbide lamp — has part — Valve. It regulates the water supply.
3. Step 3. Valve — is part of — Internal combustion engine. Valves let in the mixture and let out the gases.
4. Step 4. Internal combustion engine — is part of — Aeroplane. Piston aero engines.

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