Sled body and rope: what they have in common

1. Step 1. Sled body — is part of — Sledge. A platform.
2. Step 2. Sledge — evolved into — Cart. The wheeled cart replaced drag sledges and sleds.
3. Step 3. Cart — has part — Axle. The wheels turn on an axle.
4. Step 4. Axle — is part of — Yo-yo. The axis between the discs.
5. Step 5. Yo-yo — has part — Rope. A thread.

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