Truss and sonar: what they have in common

1. Step 1. Truss — is made of — Wrought iron. Then — wrought iron.
2. Step 2. Wrought iron — is material for — Ballast tank. The tanks are iron.
3. Step 3. Ballast tank — is part of — Submarine. Ballast tanks.
4. Step 4. Submarine — has part — Sonar. Underwater acoustics.

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