Which out of Buna-S, protein and PVC is a natural polymer ?

Explanation

To determine which of the given options (Buna-S, protein, and PVC) is a natural polymer, we can follow these steps:

### Step 1: Define Natural Polymers
Natural polymers are substances that occur naturally in the environment and are obtained from natural sources such as plants, animals, and microorganisms.

### Step 2: Analyze Each Option
1. **Buna-S**: This is a synthetic rubber made from the polymerization of styrene and butadiene. It is a man-made polymer.

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