Stethoscope and railway track: what they have in common

1. Step 1. Stethoscope — has part — Diaphragm. A diaphragm.
2. Step 2. Diaphragm — is part of — Phonograph. A diaphragm with a needle.
3. Step 3. Phonograph — is made of — Tin. The recording is on tin foil.
4. Step 4. Tin — is material for — Model railway. The first models were tinplate.
5. Step 5. Model railway — uses — Railway track. It runs on rails.

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