Rover safety bicycle and petri dish: what they have in common

1. Step 1. Rover safety bicycle — is made of — Vulcanized rubber. The tyres are rubber.
2. Step 2. Vulcanized rubber — is material for — Respirator. The mask is rubber.
3. Step 3. Respirator — evolved from — Surgical mask. A filtering mask.
4. Step 4. Surgical mask — uses — Germ theory of disease. Protection against droplets.
5. Step 5. Germ theory of disease — is used in — Petri dish. Growing bacterial cultures.

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