Mercury bulb and telephone: what they have in common

1. Step 1. Mercury bulb — is part of — Clinical thermometer. A lower ball.
2. Step 2. Clinical thermometer — evolved into — Digital thermometer. A replacement for the mercury thermometer.
3. Step 3. Digital thermometer — has part — Liquid-crystal display. The reading is on an LCD.
4. Step 4. Liquid-crystal display — is part of — Mobile phone. A screen.
5. Step 5. Mobile phone — evolved from — Telephone. A mobile phone keeps the function of a telephone, replacing the wire with a radio channel.

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