Steam carriage and pneumatic tube: what they have in common

1. Step 1. Steam carriage — has part — Watt steam engine. The steam engine.
2. Step 2. Watt steam engine — is part of — Steam locomotive. A steam locomotive is driven by a steam engine.
3. Step 3. Steam locomotive — is used in — Postal service. Mail trains.
4. Step 4. Postal service — includes — Pneumatic tube. The post.

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