Cast iron lamp post and oil well: what they have in common

1. Step 1. Cast iron lamp post — is part of — Gas lamp. A cast-iron post.
2. Step 2. Gas lamp — has part — Valve. A gas supply valve.
3. Step 3. Valve — is part of — Carburettor. A throttle valve in the carburettor sets how much fuel-air mix reaches the engine.
4. Step 4. Carburettor — uses — Petrol. It mixes petrol with air.
5. Step 5. Petrol — is made of — Crude oil. Petrol is made from crude oil.
6. Step 6. Crude oil — uses — Oil well. Oil is extracted from wells.

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