Polio vaccine and electric fan: what they have in common

1. Step 1. Polio vaccine — is a kind of — Vaccine. A vaccine.
2. Step 2. Vaccine — uses — Cold chain. Cold storage.
3. Step 3. Cold chain — uses — Refrigerator. Refrigerators.
4. Step 4. Refrigerator — has part — Thermostat. A thermostat.
5. Step 5. Thermostat — is part of — Convection oven. A thermostat.
6. Step 6. Convection oven — has part — Electric fan. A fan circulates the air.

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