Refrigerator car and syringe: what they have in common

1. Step 1. Refrigerator car — uses — Ice house. At first — ice.
2. Step 2. Ice house — evolved into — Refrigerator. The refrigerator replaced natural ice.
3. Step 3. Refrigerator — is used in — Cold chain. Refrigerators.
4. Step 4. Cold chain — is used in — Vaccine. Cold storage.
5. Step 5. Vaccine — uses — Syringe. Injections.

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