Steering wheel and rolling mill: what they have in common

1. Step 1. Steering wheel — is part of — Bobsleigh. A steering wheel.
2. Step 2. Bobsleigh — evolved from — Sledge. A sled.
3. Step 3. Sledge — evolved into — Cart. The wheeled cart replaced drag sledges and sleds.
4. Step 4. Cart — is part of — Wagonway. Wagons rolled on the rails.
5. Step 5. Wagonway — evolved into — Railway track. Cast-iron and steel rails replaced wooden ones.
6. Step 6. Railway track — uses — Rolling mill. Rails are rolled.

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