Shopping trolley and pneumatic tube: what they have in common

1. Step 1. Shopping trolley — is used in — Supermarket. Bogies.
2. Step 2. Supermarket — uses — Refrigerator. Refrigerated displays.
3. Step 3. Refrigerator — has part — Compressor. A compressor with an electric motor.
4. Step 4. Compressor — is part of — Pneumatic tube. A pressure or vacuum blower.

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