Crutches and camera: what they have in common

1. Step 1. Crutches — evolved into — Wheelchair. Mobility aids.
2. Step 2. Wheelchair — has part — Hub motor. Powered wheelchairs.
3. Step 3. Hub motor — is part of — Mars rover. Hub motors.
4. Step 4. Mars rover — evolved from — Lunokhod. Planetary rovers.
5. Step 5. Lunokhod — has part — Smartphone camera. TV cameras.
6. Step 6. Smartphone camera — evolved from — Camera. A smartphone camera keeps the layout of a camera: a lens forms an image on a light-sensitive surface.

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