Electric kettle and watt steam engine: what they have in common

1. Step 1. Electric kettle — has part — Heating element. A heating element in the base heats the water.
2. Step 2. Heating element — is part of — Espresso machine. A heater.
3. Step 3. Espresso machine — has part — Boiler. A boiler.
4. Step 4. Boiler — is part of — Watt steam engine. The boiler supplies steam.

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