Curved sickle blade and oil well: what they have in common

1. Step 1. Curved sickle blade — is part of — Sickle. A semicircular blade gathers the stems to the cut.
2. Step 2. Sickle — evolved into — Combine harvester. The machine replaced reaping by hand.
3. Step 3. Combine harvester — has part — Diesel engine. Self-propelled combines run on diesels.
4. Step 4. Diesel engine — is part of — Drilling rig. The drive.
5. Step 5. Drilling rig — is used in — Oil well. A well is drilled by a rig.

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