Biofuel and sickle: what they have in common

1. Step 1. Biofuel — is used in — Diesel engine. A diesel also runs on vegetable oil.
2. Step 2. Diesel engine — is part of — Combine harvester. Self-propelled combines run on diesels.
3. Step 3. Combine harvester — evolved from — Sickle. The machine replaced reaping by hand.

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