Metric system and tank: what they have in common

1. Step 1. Metric system — is used in — Standard kilogram. The unit of mass.
2. Step 2. Standard kilogram — is made of — Platinum. A platinum–iridium alloy.
3. Step 3. Platinum — is material for — Catalytic converter. Platinum-group metals.
4. Step 4. Catalytic converter — is part of — Car. Modern cars have a catalytic converter.
5. Step 5. Car — evolved into — Armoured car. A car with armour.
6. Step 6. Armoured car — evolved into — Tank. The tank combined the armour of an armoured car with the off-road ability of tracks.

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