Heat pump and syringe: what they have in common

1. Step 1. Heat pump — works like — Refrigerator. A heat pump is a refrigerator that heats the house.
2. Step 2. Refrigerator — is used in — Cold chain. Refrigerators.
3. Step 3. Cold chain — is used in — Vaccine. Cold storage.
4. Step 4. Vaccine — uses — Syringe. Injections.

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