Railway coupling and aerosol can: what they have in common

1. Step 1. Railway coupling — is part of — Electric locomotive. An electric locomotive pulls its wagons through a coupling.
2. Step 2. Electric locomotive — is part of — Panama Canal. Electric “mules” tow the ships through the locks.
3. Step 3. Panama Canal — has part — Canal lock. Locks.
4. Step 4. Canal lock — has part — Valve. Sluice gates.
5. Step 5. Valve — is part of — Aerosol can. A valve.

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