Pesticide and rock drill: what they have in common

1. Step 1. Pesticide — uses — Aerosol can. In 1941 insecticide began to be sprayed from aerosol cans, the "bug bombs" made for soldiers; after the war the same can was used for hair spray.
2. Step 2. Aerosol can — has part — Valve. A valve.
3. Step 3. Valve — is part of — Gas lamp. A gas supply valve.
4. Step 4. Gas lamp — evolved into — Street light. Gas lamps.
5. Step 5. Street light — is part of — Tunnel. Lighting.
6. Step 6. Tunnel — uses — Rock drill. Driving the Mont Cenis tunnel.

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