Electric fan and fuel cell: what they have in common

1. Step 1. Electric fan — has part — Propeller. The blades.
2. Step 2. Propeller — is part of — Airship. Air propellers.
3. Step 3. Airship — uses — Hydrogen. Zeppelins were filled with hydrogen.
4. Step 4. Hydrogen — is used in — Fuel cell. The fuel is hydrogen.

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