Lever and rock drill: what they have in common

1. Step 1. Lever — is used in — Pantograph. A hinged linkage presses the shoe against the wire.
2. Step 2. Pantograph — is part of — Electric locomotive. Current is collected by a pantograph.
3. Step 3. Electric locomotive — is used in — Metro. The first lines were steam-operated; electric trains since 1890.
4. Step 4. Metro — uses — Tunnel. Tunnels.
5. Step 5. Tunnel — uses — Rock drill. Driving the Mont Cenis tunnel.

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