Duralumin and gutenberg printing press: what they have in common

1. Step 1. Duralumin — is material for — Airship. The frames of zeppelins.
2. Step 2. Airship — evolved from — Hot air balloon. A steerable balloon.
3. Step 3. Hot air balloon — is made of — Paper. It was lined with paper on the inside.
4. Step 4. Paper — is used in — Gutenberg printing press. The impression is made on paper.

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