Stadium and steam locomotive: what they have in common

1. Step 1. Stadium — has part — Retractable roof. A retractable roof.
2. Step 2. Retractable roof — has part — Truss. Trusses.
3. Step 3. Truss — is part of — Truss bridge. Trusses.
4. Step 4. Truss bridge — uses — Railway track. Railway bridges.
5. Step 5. Railway track — is used in — Steam locomotive. It runs on rails.

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