Sonar and plough: what they have in common

1. Step 1. Sonar — is part of — Submarine. Underwater acoustics.
2. Step 2. Submarine — has part — Diesel engine. Diesel-electric submarines.
3. Step 3. Diesel engine — is part of — Tractor. A diesel.
4. Step 4. Tractor — uses — Steel plough. Ploughing with a tractor.
5. Step 5. Steel plough — evolved from — Plough. A steel share.

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