Barbed harpoon head and solar panel: what they have in common

1. Step 1. Barbed harpoon head — is part of — Harpoon. Barbs keep the prey from slipping off.
2. Step 2. Harpoon — has part — Rope. A line connects the head to the hunter.
3. Step 3. Rope — is used in — Pulley. A rope runs over the pulley.
4. Step 4. Pulley — has part — Wheel. A pulley is a wheel with a groove for a rope.
5. Step 5. Wheel — is part of — Lunokhod. Wheels.
6. Step 6. Lunokhod — has part — Solar panel. A solar panel.

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