Comb and conveyor belt: what they have in common

1. Step 1. Comb — is made of — Bone. Ancient combs were carved from bone and antler.
2. Step 2. Bone — is material for — Ice skates. The first skates were horse bones with a polished side.
3. Step 3. Ice skates — evolved into — Roller skates. Skates for dry land.
4. Step 4. Roller skates — has part — Ball bearing. Bearings.
5. Step 5. Ball bearing — is part of — Conveyor belt. The rollers turn on bearings.

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