Towel and tunnelling shield: what they have in common

1. Step 1. Towel — is made of — Cotton. Cotton.
2. Step 2. Cotton — is material for — Wright Flyer. The covering is muslin.
3. Step 3. Wright Flyer — uses — Railway track. The Flyer had no wheels: it took off along a wooden rail.
4. Step 4. Railway track — is used in — Metro. It runs on rails.
5. Step 5. Metro — uses — Tunnelling shield. Metro tunnels were built with shields.

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