Shafts for harnessing a horse and submarine: what they have in common

1. Step 1. Shafts for harnessing a horse — is part of — Sledge. A rod.
2. Step 2. Sledge — evolved into — Cart. The wheeled cart replaced drag sledges and sleds.
3. Step 3. Cart — evolved into — Chariot. A chariot is a lightened cart.
4. Step 4. Chariot — is made of — Leather. The floor was woven from leather straps.
5. Step 5. Leather — is material for — Submarine. It was covered with leather.

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