What is causative agent of simple goitre?

Explanation

### Step-by-Step Solution:

1. **Identify the Condition**: The question asks about the causative agent of simple goitre. Goitre is a condition characterized by the enlargement of the thyroid gland.

2. **Understand the Role of the Thyroid Gland**: The thyroid gland is crucial for regulating metabolism and producing hormones. It is the gland that is affected in the case of goitre.

3. **Recognize the Importance of Iodine**: Iodine is an essential nutrient that the thyroid gland requires to produce thyroid hormones. A deficiency in iodine is directly linked to the development of goitre.

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