Rubber crutch tip and plough: what they have in common

1. Step 1. Rubber crutch tip — is part of — Crutches. It prevents slipping.
2. Step 2. Crutches — evolved into — Wheelchair. Mobility aids.
3. Step 3. Wheelchair — has part — Wheel. Wheels.
4. Step 4. Wheel — is part of — Stagecoach. On four wheels.
5. Step 5. Stagecoach — uses — Horse collar. It is pulled by horses.
6. Step 6. Horse collar — is used in — Plough. The horse collar made ploughing with horses possible.

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