Threshing machine and sonar: what they have in common

1. Step 1. Threshing machine — evolved into — Combine harvester. Combining machines.
2. Step 2. Combine harvester — has part — Diesel engine. Self-propelled combines run on diesels.
3. Step 3. Diesel engine — is part of — Submarine. Diesel-electric submarines.
4. Step 4. Submarine — has part — Sonar. Underwater acoustics.

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