Platinum-iridium cylinder and fuel cell: what they have in common

1. Step 1. Platinum-iridium cylinder — is part of — Standard kilogram. A 39 × 39 mm cylinder.
2. Step 2. Standard kilogram — is made of — Platinum. A platinum–iridium alloy.
3. Step 3. Platinum — is material for — Fuel cell. A platinum catalyst.

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