Give an example of a plant which came into India as a contaminant and is a cause of pollen allergy.

Explanation

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks for an example of a plant that came into India as a contaminant and is known to cause pollen allergy.

2. **Determine the Plant**: The plant that fits this description is **Parthenium**. It is commonly known as **Carrot Grass**.

3. **Understand the Nature of Contaminants**: Parthenium is classified as an unwanted plant or a contaminant. Contaminants are typically non-native species that can disrupt local ecosystems.

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