Index card and centrifugal pump: what they have in common

1. Step 1. Index card — is made of — Paper. Paper.
2. Step 2. Paper — is material for — Rocket. The first rockets were paper tubes filled with gunpowder.
3. Step 3. Rocket — evolved into — Liquid-propellant rocket engine. Goddard switched to liquid fuel.
4. Step 4. Liquid-propellant rocket engine — has part — Centrifugal pump. Turbopumps deliver the propellant.

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