Backpack and petri dish: what they have in common

1. Step 1. Backpack — is made of — Nylon. Nylon.
2. Step 2. Nylon — evolved into — Polyester. The next synthetic fibre.
3. Step 3. Polyester — is a kind of — PET. Polyester fibre is PET.
4. Step 4. PET — is material for — Plastic bottle. A PET bottle.
5. Step 5. Plastic bottle — has part — Pot lid. A polyethylene lid.
6. Step 6. Pot lid — is part of — Petri dish. A cap.

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