Kettle body and boiler: what they have in common

1. Step 1. Kettle body — is part of — Kettle. A container for water.
2. Step 2. Kettle — evolved into — Electric kettle. A kettle with a heater.
3. Step 3. Electric kettle — has part — Heating element. A heating element in the base heats the water.
4. Step 4. Heating element — is part of — Espresso machine. A heater.
5. Step 5. Espresso machine — has part — Boiler. A boiler.

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