Tunnel portal and kite: what they have in common

1. Step 1. Tunnel portal — is part of — Tunnel. Tunnel portals.
2. Step 2. Tunnel — uses — Mine ventilation. Ventilation.
3. Step 3. Mine ventilation — has part — Electric fan. Fans.
4. Step 4. Electric fan — is part of — Wind tunnel. A fan.
5. Step 5. Wind tunnel — uses — Lift. Measuring lift.
6. Step 6. Lift — is used in — Kite. A kite is held up by lift.

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