Quern and tank: what they have in common

1. Step 1. Quern — evolved into — Threshing machine. Mechanizing the processing of grain.
2. Step 2. Threshing machine — evolved into — Combine harvester. Combining machines.
3. Step 3. Combine harvester — has part — Diesel engine. Self-propelled combines run on diesels.
4. Step 4. Diesel engine — is part of — Tank. Most modern tanks are powered by a diesel (the Mark I had a petrol engine).

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