Revolving door and parachute: what they have in common

1. Step 1. Revolving door — has part — Ball bearing. The axis.
2. Step 2. Ball bearing — is part of — Wheelchair. Bearings.
3. Step 3. Wheelchair — has part — Spoke. Spoked wheels.
4. Step 4. Spoke — is part of — Umbrella. Ribs hold the canopy.
5. Step 5. Umbrella — is made of — Silk. The canopy is made of silk.
6. Step 6. Silk — is material for — Parachute. The canopy is silk.

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