Oil cracking and cannon: what they have in common

1. Step 1. Oil cracking — is used in — Petrol. More petrol from crude oil.
2. Step 2. Petrol — is made of — Crude oil. Petrol is made from crude oil.
3. Step 3. Crude oil — uses — Oil well. Oil is extracted from wells.
4. Step 4. Oil well — is made of — Wrought iron. The casing pipes are iron.
5. Step 5. Wrought iron — is material for — Ironclad. The armour is wrought iron.
6. Step 6. Ironclad — has part — Cannon. Artillery.

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