Camera obscura and railway track: what they have in common

1. Step 1. Camera obscura — evolved into — Camera. A camera is a camera obscura with a light-sensitive layer.
2. Step 2. Camera — has part — Photographic flash. A flash.
3. Step 3. Photographic flash — has part — Capacitor. Energy is stored in a capacitor.
4. Step 4. Capacitor — is made of — Tin. The plates are made of tin foil.
5. Step 5. Tin — is material for — Model railway. The first models were tinplate.
6. Step 6. Model railway — uses — Railway track. It runs on rails.

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