Carabiner and radio: what they have in common

1. Step 1. Carabiner — has part — Spring. A gate.
2. Step 2. Spring — is part of — Rotary dial. A return spring.
3. Step 3. Rotary dial — is part of — Telephone. A dial.
4. Step 4. Telephone — evolved into — Mobile phone. A mobile phone keeps the function of a telephone, replacing the wire with a radio channel.
5. Step 5. Mobile phone — evolved from — Radio. Mobile communication is a development of radiotelephony.

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