First aid kit and tunnelling shield: what they have in common

1. Step 1. First aid kit — is made of — Tin. A tin box.
2. Step 2. Tin — is material for — Model railway. The first models were tinplate.
3. Step 3. Model railway — uses — Railway track. It runs on rails.
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.

Open Evothings