Wheelchair and sewage treatment plant: what they have in common

1. Step 1. Wheelchair — has part — Ball bearing. Bearings.
2. Step 2. Ball bearing — is part of — Bogie. Axle boxes with roller bearings.
3. Step 3. Bogie — is part of — Refrigerator car. Bogies.
4. Step 4. Refrigerator car — has part — Compressor. A refrigeration unit.
5. Step 5. Compressor — is part of — Sewage treatment plant. Blowers supply oxygen to the microbes.

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