Drill steel rod with bit and solar panel: what they have in common

1. Step 1. Drill steel rod with bit — is part of — Rock drill. A steel rod with a bit.
2. Step 2. Rock drill — is used in — Tunnel. Driving the Mont Cenis tunnel.
3. Step 3. Tunnel — has part — Street light. Lighting.
4. Step 4. Street light — has part — Photoresistor. Switching on at dusk.
5. Step 5. Photoresistor — uses — Photovoltaic effect. Photoconductivity.
6. Step 6. Photovoltaic effect — is used in — Solar panel. The photoelectric effect in a semiconductor.

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