Blood groups and aeroplane: what they have in common

1. Step 1. Blood groups — is used in — Blood bank. Recording blood groups.
2. Step 2. Blood bank — uses — Refrigerator. Cold storage.
3. Step 3. Refrigerator — has part — Compressor. A compressor with an electric motor.
4. Step 4. Compressor — is part of — Pressurized cabin. Air is bled from the engine compressors.
5. Step 5. Pressurized cabin — is part of — Jet airliner. A pressurized cabin.
6. Step 6. Jet airliner — evolved from — Aeroplane. A jet aircraft.

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