_________ hormone is responsible for regulating the utilization of nutrients such as proteins, carbohydrates and fats in the body.
a) Thyroxine
b) Growth
c) Calcitonin
d) Triiodothyronine

Options

A. Thyroxine
B. Growth
C. Calcitonin
D. Triiodothyronine

Answer

To solve the question regarding which hormone is responsible for regulating the utilization of nutrients such as proteins, carbohydrates, and fats in the body, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for a hormone that regulates the utilization of nutrients in the body. We need to identify which of the given options fits this description.

2. **Analyzing the Options**:
- **a) Thyroxine**: This hormone, also known as T4, is produced by the thyroid gland and plays a significant role in metabolism, including the utilization of proteins, carbohydrates, and fats.
- **b) Growth Hormone**: This hormone is primarily responsible for growth and development in the body, not specifically for nutrient utilization.
- **c) Calcitonin**: This hormone helps regulate calcium levels in the blood and is not involved in the metabolism of nutrients.
- **d) Triiodothyronine (T3)**: This hormone is also produced by the thyroid gland and is involved in metabolism, but it is derived from thyroxine (T4) and has a shorter lifespan.

3. **Identifying the Most Relevant Hormone**: Between thyroxine (T4) and triiodothyronine (T3), both are involved in regulating metabolism. However, thyroxine (T4) has a longer duration of action and is the primary hormone responsible for regulating the metabolism of nutrients over a longer period.

4. **Conclusion**: Based on the analysis, the hormone responsible for regulating the utilization of nutrients such as proteins, carbohydrates, and fats in the body is **Thyroxine (T4)**.

### Final Answer:
**a) Thyroxine**

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