Spectacle frame and tank: what they have in common

1. Step 1. Spectacle frame — is made of — Bone. The first frames were made of bone and horn.
2. Step 2. Bone — is material for — Dentures. With teeth made of bone or real teeth.
3. Step 3. Dentures — is made of — Porcelain. Porcelain teeth.
4. Step 4. Porcelain — is material for — Composite armour. Ceramic layers.
5. Step 5. Composite armour — is part of — Tank. Multi-layer armour.

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