Combustion and zip: what they have in common

1. Step 1. Combustion — is used in — Hot air balloon. A fire heated the air inside.
2. Step 2. Hot air balloon — is made of — Nylon. A light, strong envelope fabric.
3. Step 3. Nylon — is material for — Backpack. Nylon.
4. Step 4. Backpack — has part — Zip. Zips.

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